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/- | |
Copyright (c) 2015, 2017 Jeremy Avigad. All rights reserved. | |
Released under Apache 2.0 license as described in the file LICENSE. | |
Authors: Jeremy Avigad, Robert Y. Lewis, Johannes Hölzl, Mario Carneiro, Sébastien Gouëzel | |
-/ | |
import data.int.interval | |
import tactic.positivity | |
import topology.algebra.order.compact | |
import topology.metric_space.emetric_space | |
import topology.bornology.constructions | |
import topology.uniform_space.complete_separated | |
/-! | |
# Metric spaces | |
This file defines metric spaces. Many definitions and theorems expected | |
on metric spaces are already introduced on uniform spaces and topological spaces. | |
For example: open and closed sets, compactness, completeness, continuity and uniform continuity | |
## Main definitions | |
* `has_dist α`: Endows a space `α` with a function `dist a b`. | |
* `pseudo_metric_space α`: A space endowed with a distance function, which can | |
be zero even if the two elements are non-equal. | |
* `metric.ball x ε`: The set of all points `y` with `dist y x < ε`. | |
* `metric.bounded s`: Whether a subset of a `pseudo_metric_space` is bounded. | |
* `metric_space α`: A `pseudo_metric_space` with the guarantee `dist x y = 0 → x = y`. | |
Additional useful definitions: | |
* `nndist a b`: `dist` as a function to the non-negative reals. | |
* `metric.closed_ball x ε`: The set of all points `y` with `dist y x ≤ ε`. | |
* `metric.sphere x ε`: The set of all points `y` with `dist y x = ε`. | |
* `proper_space α`: A `pseudo_metric_space` where all closed balls are compact. | |
* `metric.diam s` : The `supr` of the distances of members of `s`. | |
Defined in terms of `emetric.diam`, for better handling of the case when it should be infinite. | |
TODO (anyone): Add "Main results" section. | |
## Implementation notes | |
Since a lot of elementary properties don't require `eq_of_dist_eq_zero` we start setting up the | |
theory of `pseudo_metric_space`, where we don't require `dist x y = 0 → x = y` and we specialize | |
to `metric_space` at the end. | |
## Tags | |
metric, pseudo_metric, dist | |
-/ | |
open set filter topological_space bornology | |
open_locale uniformity topological_space big_operators filter nnreal ennreal | |
universes u v w | |
variables {α : Type u} {β : Type v} {X : Type*} | |
/-- Construct a uniform structure core from a distance function and metric space axioms. | |
This is a technical construction that can be immediately used to construct a uniform structure | |
from a distance function and metric space axioms but is also useful when discussing | |
metrizable topologies, see `pseudo_metric_space.of_metrizable`. -/ | |
def uniform_space.core_of_dist {α : Type*} (dist : α → α → ℝ) | |
(dist_self : ∀ x : α, dist x x = 0) | |
(dist_comm : ∀ x y : α, dist x y = dist y x) | |
(dist_triangle : ∀ x y z : α, dist x z ≤ dist x y + dist y z) : uniform_space.core α := | |
{ uniformity := (⨅ ε>0, 𝓟 {p:α×α | dist p.1 p.2 < ε}), | |
refl := le_infi $ assume ε, le_infi $ | |
by simp [set.subset_def, id_rel, dist_self, (>)] {contextual := tt}, | |
comp := le_infi $ assume ε, le_infi $ assume h, lift'_le | |
(mem_infi_of_mem (ε / 2) $ mem_infi_of_mem (div_pos h zero_lt_two) (subset.refl _)) $ | |
have ∀ (a b c : α), dist a c < ε / 2 → dist c b < ε / 2 → dist a b < ε, | |
from assume a b c hac hcb, | |
calc dist a b ≤ dist a c + dist c b : dist_triangle _ _ _ | |
... < ε / 2 + ε / 2 : add_lt_add hac hcb | |
... = ε : by rw [div_add_div_same, add_self_div_two], | |
by simpa [comp_rel], | |
symm := tendsto_infi.2 $ assume ε, tendsto_infi.2 $ assume h, | |
tendsto_infi' ε $ tendsto_infi' h $ tendsto_principal_principal.2 $ by simp [dist_comm] } | |
/-- Construct a uniform structure from a distance function and metric space axioms -/ | |
def uniform_space_of_dist | |
(dist : α → α → ℝ) | |
(dist_self : ∀ x : α, dist x x = 0) | |
(dist_comm : ∀ x y : α, dist x y = dist y x) | |
(dist_triangle : ∀ x y z : α, dist x z ≤ dist x y + dist y z) : uniform_space α := | |
uniform_space.of_core (uniform_space.core_of_dist dist dist_self dist_comm dist_triangle) | |
/-- This is an internal lemma used to construct a bornology from a metric in `bornology.of_dist`. -/ | |
private lemma bounded_iff_aux {α : Type*} (dist : α → α → ℝ) | |
(dist_comm : ∀ x y : α, dist x y = dist y x) | |
(dist_triangle : ∀ x y z : α, dist x z ≤ dist x y + dist y z) | |
(s : set α) (a : α) : | |
(∃ c, ∀ ⦃x⦄, x ∈ s → ∀ ⦃y⦄, y ∈ s → dist x y ≤ c) ↔ (∃ r, ∀ ⦃x⦄, x ∈ s → dist x a ≤ r) := | |
begin | |
split; rintro ⟨C, hC⟩, | |
{ rcases s.eq_empty_or_nonempty with rfl | ⟨x, hx⟩, | |
{ exact ⟨0, by simp⟩ }, | |
{ exact ⟨C + dist x a, λ y hy, | |
(dist_triangle y x a).trans (add_le_add_right (hC hy hx) _)⟩ } }, | |
{ exact ⟨C + C, λ x hx y hy, | |
(dist_triangle x a y).trans (add_le_add (hC hx) (by {rw dist_comm, exact hC hy}))⟩ } | |
end | |
/-- Construct a bornology from a distance function and metric space axioms. -/ | |
def bornology.of_dist {α : Type*} (dist : α → α → ℝ) | |
(dist_self : ∀ x : α, dist x x = 0) | |
(dist_comm : ∀ x y : α, dist x y = dist y x) | |
(dist_triangle : ∀ x y z : α, dist x z ≤ dist x y + dist y z) : | |
bornology α := | |
bornology.of_bounded | |
{ s : set α | ∃ C, ∀ ⦃x⦄, x ∈ s → ∀ ⦃y⦄, y ∈ s → dist x y ≤ C } | |
⟨0, λ x hx y, hx.elim⟩ | |
(λ s ⟨c, hc⟩ t h, ⟨c, λ x hx y hy, hc (h hx) (h hy)⟩) | |
(λ s hs t ht, | |
begin | |
rcases s.eq_empty_or_nonempty with rfl | ⟨z, hz⟩, | |
{ exact (empty_union t).symm ▸ ht }, | |
{ simp only [λ u, bounded_iff_aux dist dist_comm dist_triangle u z] at hs ht ⊢, | |
rcases ⟨hs, ht⟩ with ⟨⟨r₁, hr₁⟩, ⟨r₂, hr₂⟩⟩, | |
exact ⟨max r₁ r₂, λ x hx, or.elim hx | |
(λ hx', (hr₁ hx').trans (le_max_left _ _)) | |
(λ hx', (hr₂ hx').trans (le_max_right _ _))⟩ } | |
end) | |
(λ z, ⟨0, λ x hx y hy, | |
by { rw [eq_of_mem_singleton hx, eq_of_mem_singleton hy], exact (dist_self z).le }⟩) | |
/-- The distance function (given an ambient metric space on `α`), which returns | |
a nonnegative real number `dist x y` given `x y : α`. -/ | |
@[ext] class has_dist (α : Type*) := (dist : α → α → ℝ) | |
export has_dist (dist) | |
-- the uniform structure and the emetric space structure are embedded in the metric space structure | |
-- to avoid instance diamond issues. See Note [forgetful inheritance]. | |
/-- This is an internal lemma used inside the default of `pseudo_metric_space.edist`. -/ | |
private theorem pseudo_metric_space.dist_nonneg' {α} {x y : α} (dist : α → α → ℝ) | |
(dist_self : ∀ x : α, dist x x = 0) | |
(dist_comm : ∀ x y : α, dist x y = dist y x) | |
(dist_triangle : ∀ x y z : α, dist x z ≤ dist x y + dist y z): 0 ≤ dist x y := | |
have 2 * dist x y ≥ 0, | |
from calc 2 * dist x y = dist x y + dist y x : by rw [dist_comm x y, two_mul] | |
... ≥ 0 : by rw ← dist_self x; apply dist_triangle, | |
nonneg_of_mul_nonneg_right this zero_lt_two | |
/-- This tactic is used to populate `pseudo_metric_space.edist_dist` when the default `edist` is | |
used. -/ | |
protected meta def pseudo_metric_space.edist_dist_tac : tactic unit := | |
tactic.intros >> `[exact (ennreal.of_real_eq_coe_nnreal _).symm <|> control_laws_tac] | |
/-- Metric space | |
Each metric space induces a canonical `uniform_space` and hence a canonical `topological_space`. | |
This is enforced in the type class definition, by extending the `uniform_space` structure. When | |
instantiating a `metric_space` structure, the uniformity fields are not necessary, they will be | |
filled in by default. In the same way, each metric space induces an emetric space structure. | |
It is included in the structure, but filled in by default. | |
-/ | |
class pseudo_metric_space (α : Type u) extends has_dist α : Type u := | |
(dist_self : ∀ x : α, dist x x = 0) | |
(dist_comm : ∀ x y : α, dist x y = dist y x) | |
(dist_triangle : ∀ x y z : α, dist x z ≤ dist x y + dist y z) | |
(edist : α → α → ℝ≥0∞ := λ x y, | |
@coe (ℝ≥0) _ _ ⟨dist x y, pseudo_metric_space.dist_nonneg' _ ‹_› ‹_› ‹_›⟩) | |
(edist_dist : ∀ x y : α, | |
edist x y = ennreal.of_real (dist x y) . pseudo_metric_space.edist_dist_tac) | |
(to_uniform_space : uniform_space α := uniform_space_of_dist dist dist_self dist_comm dist_triangle) | |
(uniformity_dist : 𝓤 α = ⨅ ε>0, 𝓟 {p:α×α | dist p.1 p.2 < ε} . control_laws_tac) | |
(to_bornology : bornology α := bornology.of_dist dist dist_self dist_comm dist_triangle) | |
(cobounded_sets : (bornology.cobounded α).sets = | |
{ s | ∃ C, ∀ ⦃x⦄, x ∈ sᶜ → ∀ ⦃y⦄, y ∈ sᶜ → dist x y ≤ C } . control_laws_tac) | |
/-- Two pseudo metric space structures with the same distance function coincide. -/ | |
@[ext] lemma pseudo_metric_space.ext {α : Type*} {m m' : pseudo_metric_space α} | |
(h : m.to_has_dist = m'.to_has_dist) : m = m' := | |
begin | |
unfreezingI { rcases m, rcases m' }, | |
dsimp at h, | |
unfreezingI { subst h }, | |
congr, | |
{ ext x y : 2, | |
dsimp at m_edist_dist m'_edist_dist, | |
simp [m_edist_dist, m'_edist_dist] }, | |
{ dsimp at m_uniformity_dist m'_uniformity_dist, | |
rw ← m'_uniformity_dist at m_uniformity_dist, | |
exact uniform_space_eq m_uniformity_dist }, | |
{ ext1, | |
dsimp at m_cobounded_sets m'_cobounded_sets, | |
rw ← m'_cobounded_sets at m_cobounded_sets, | |
exact filter_eq m_cobounded_sets } | |
end | |
variables [pseudo_metric_space α] | |
attribute [priority 100, instance] pseudo_metric_space.to_uniform_space | |
attribute [priority 100, instance] pseudo_metric_space.to_bornology | |
@[priority 200] -- see Note [lower instance priority] | |
instance pseudo_metric_space.to_has_edist : has_edist α := ⟨pseudo_metric_space.edist⟩ | |
/-- Construct a pseudo-metric space structure whose underlying topological space structure | |
(definitionally) agrees which a pre-existing topology which is compatible with a given distance | |
function. -/ | |
def pseudo_metric_space.of_metrizable {α : Type*} [topological_space α] (dist : α → α → ℝ) | |
(dist_self : ∀ x : α, dist x x = 0) | |
(dist_comm : ∀ x y : α, dist x y = dist y x) | |
(dist_triangle : ∀ x y z : α, dist x z ≤ dist x y + dist y z) | |
(H : ∀ s : set α, is_open s ↔ ∀ x ∈ s, ∃ ε > 0, ∀ y, dist x y < ε → y ∈ s) : | |
pseudo_metric_space α := | |
{ dist := dist, | |
dist_self := dist_self, | |
dist_comm := dist_comm, | |
dist_triangle := dist_triangle, | |
to_uniform_space := { is_open_uniformity := begin | |
dsimp only [uniform_space.core_of_dist], | |
intros s, | |
change is_open s ↔ _, | |
rw H s, | |
refine forall₂_congr (λ x x_in, _), | |
erw (has_basis_binfi_principal _ nonempty_Ioi).mem_iff, | |
{ refine exists₂_congr (λ ε ε_pos, _), | |
simp only [prod.forall, set_of_subset_set_of], | |
split, | |
{ rintros h _ y H rfl, | |
exact h y H }, | |
{ intros h y hxy, | |
exact h _ _ hxy rfl } }, | |
{ exact λ r (hr : 0 < r) p (hp : 0 < p), ⟨min r p, lt_min hr hp, | |
λ x (hx : dist _ _ < _), lt_of_lt_of_le hx (min_le_left r p), | |
λ x (hx : dist _ _ < _), lt_of_lt_of_le hx (min_le_right r p)⟩ }, | |
{ apply_instance } | |
end, | |
..uniform_space.core_of_dist dist dist_self dist_comm dist_triangle }, | |
uniformity_dist := rfl, | |
to_bornology := bornology.of_dist dist dist_self dist_comm dist_triangle, | |
cobounded_sets := rfl } | |
@[simp] theorem dist_self (x : α) : dist x x = 0 := pseudo_metric_space.dist_self x | |
theorem dist_comm (x y : α) : dist x y = dist y x := pseudo_metric_space.dist_comm x y | |
theorem edist_dist (x y : α) : edist x y = ennreal.of_real (dist x y) := | |
pseudo_metric_space.edist_dist x y | |
theorem dist_triangle (x y z : α) : dist x z ≤ dist x y + dist y z := | |
pseudo_metric_space.dist_triangle x y z | |
theorem dist_triangle_left (x y z : α) : dist x y ≤ dist z x + dist z y := | |
by rw dist_comm z; apply dist_triangle | |
theorem dist_triangle_right (x y z : α) : dist x y ≤ dist x z + dist y z := | |
by rw dist_comm y; apply dist_triangle | |
lemma dist_triangle4 (x y z w : α) : | |
dist x w ≤ dist x y + dist y z + dist z w := | |
calc dist x w ≤ dist x z + dist z w : dist_triangle x z w | |
... ≤ (dist x y + dist y z) + dist z w : add_le_add_right (dist_triangle x y z) _ | |
lemma dist_triangle4_left (x₁ y₁ x₂ y₂ : α) : | |
dist x₂ y₂ ≤ dist x₁ y₁ + (dist x₁ x₂ + dist y₁ y₂) := | |
by { rw [add_left_comm, dist_comm x₁, ← add_assoc], apply dist_triangle4 } | |
lemma dist_triangle4_right (x₁ y₁ x₂ y₂ : α) : | |
dist x₁ y₁ ≤ dist x₁ x₂ + dist y₁ y₂ + dist x₂ y₂ := | |
by { rw [add_right_comm, dist_comm y₁], apply dist_triangle4 } | |
/-- The triangle (polygon) inequality for sequences of points; `finset.Ico` version. -/ | |
lemma dist_le_Ico_sum_dist (f : ℕ → α) {m n} (h : m ≤ n) : | |
dist (f m) (f n) ≤ ∑ i in finset.Ico m n, dist (f i) (f (i + 1)) := | |
begin | |
revert n, | |
apply nat.le_induction, | |
{ simp only [finset.sum_empty, finset.Ico_self, dist_self] }, | |
{ assume n hn hrec, | |
calc dist (f m) (f (n+1)) ≤ dist (f m) (f n) + dist _ _ : dist_triangle _ _ _ | |
... ≤ ∑ i in finset.Ico m n, _ + _ : add_le_add hrec le_rfl | |
... = ∑ i in finset.Ico m (n+1), _ : | |
by rw [nat.Ico_succ_right_eq_insert_Ico hn, finset.sum_insert, add_comm]; simp } | |
end | |
/-- The triangle (polygon) inequality for sequences of points; `finset.range` version. -/ | |
lemma dist_le_range_sum_dist (f : ℕ → α) (n : ℕ) : | |
dist (f 0) (f n) ≤ ∑ i in finset.range n, dist (f i) (f (i + 1)) := | |
nat.Ico_zero_eq_range ▸ dist_le_Ico_sum_dist f (nat.zero_le n) | |
/-- A version of `dist_le_Ico_sum_dist` with each intermediate distance replaced | |
with an upper estimate. -/ | |
lemma dist_le_Ico_sum_of_dist_le {f : ℕ → α} {m n} (hmn : m ≤ n) | |
{d : ℕ → ℝ} (hd : ∀ {k}, m ≤ k → k < n → dist (f k) (f (k + 1)) ≤ d k) : | |
dist (f m) (f n) ≤ ∑ i in finset.Ico m n, d i := | |
le_trans (dist_le_Ico_sum_dist f hmn) $ | |
finset.sum_le_sum $ λ k hk, hd (finset.mem_Ico.1 hk).1 (finset.mem_Ico.1 hk).2 | |
/-- A version of `dist_le_range_sum_dist` with each intermediate distance replaced | |
with an upper estimate. -/ | |
lemma dist_le_range_sum_of_dist_le {f : ℕ → α} (n : ℕ) | |
{d : ℕ → ℝ} (hd : ∀ {k}, k < n → dist (f k) (f (k + 1)) ≤ d k) : | |
dist (f 0) (f n) ≤ ∑ i in finset.range n, d i := | |
nat.Ico_zero_eq_range ▸ dist_le_Ico_sum_of_dist_le (zero_le n) (λ _ _, hd) | |
theorem swap_dist : function.swap (@dist α _) = dist := | |
by funext x y; exact dist_comm _ _ | |
theorem abs_dist_sub_le (x y z : α) : |dist x z - dist y z| ≤ dist x y := | |
abs_sub_le_iff.2 | |
⟨sub_le_iff_le_add.2 (dist_triangle _ _ _), | |
sub_le_iff_le_add.2 (dist_triangle_left _ _ _)⟩ | |
theorem dist_nonneg {x y : α} : 0 ≤ dist x y := | |
pseudo_metric_space.dist_nonneg' dist dist_self dist_comm dist_triangle | |
section | |
open tactic tactic.positivity | |
/-- Extension for the `positivity` tactic: distances are nonnegative. -/ | |
@[positivity] | |
meta def _root_.tactic.positivity_dist : expr → tactic strictness | |
| `(dist %%a %%b) := nonnegative <$> mk_app ``dist_nonneg [a, b] | |
| _ := failed | |
end | |
@[simp] theorem abs_dist {a b : α} : |dist a b| = dist a b := | |
abs_of_nonneg dist_nonneg | |
/-- A version of `has_dist` that takes value in `ℝ≥0`. -/ | |
class has_nndist (α : Type*) := (nndist : α → α → ℝ≥0) | |
export has_nndist (nndist) | |
/-- Distance as a nonnegative real number. -/ | |
@[priority 100] -- see Note [lower instance priority] | |
instance pseudo_metric_space.to_has_nndist : has_nndist α := ⟨λ a b, ⟨dist a b, dist_nonneg⟩⟩ | |
/--Express `nndist` in terms of `edist`-/ | |
lemma nndist_edist (x y : α) : nndist x y = (edist x y).to_nnreal := | |
by simp [nndist, edist_dist, real.to_nnreal, max_eq_left dist_nonneg, ennreal.of_real] | |
/--Express `edist` in terms of `nndist`-/ | |
lemma edist_nndist (x y : α) : edist x y = ↑(nndist x y) := | |
by { simpa only [edist_dist, ennreal.of_real_eq_coe_nnreal dist_nonneg] } | |
@[simp, norm_cast] lemma coe_nnreal_ennreal_nndist (x y : α) : ↑(nndist x y) = edist x y := | |
(edist_nndist x y).symm | |
@[simp, norm_cast] lemma edist_lt_coe {x y : α} {c : ℝ≥0} : | |
edist x y < c ↔ nndist x y < c := | |
by rw [edist_nndist, ennreal.coe_lt_coe] | |
@[simp, norm_cast] lemma edist_le_coe {x y : α} {c : ℝ≥0} : | |
edist x y ≤ c ↔ nndist x y ≤ c := | |
by rw [edist_nndist, ennreal.coe_le_coe] | |
/--In a pseudometric space, the extended distance is always finite-/ | |
lemma edist_lt_top {α : Type*} [pseudo_metric_space α] (x y : α) : edist x y < ⊤ := | |
(edist_dist x y).symm ▸ ennreal.of_real_lt_top | |
/--In a pseudometric space, the extended distance is always finite-/ | |
lemma edist_ne_top (x y : α) : edist x y ≠ ⊤ := (edist_lt_top x y).ne | |
/--`nndist x x` vanishes-/ | |
@[simp] lemma nndist_self (a : α) : nndist a a = 0 := (nnreal.coe_eq_zero _).1 (dist_self a) | |
/--Express `dist` in terms of `nndist`-/ | |
lemma dist_nndist (x y : α) : dist x y = ↑(nndist x y) := rfl | |
@[simp, norm_cast] lemma coe_nndist (x y : α) : ↑(nndist x y) = dist x y := | |
(dist_nndist x y).symm | |
@[simp, norm_cast] lemma dist_lt_coe {x y : α} {c : ℝ≥0} : | |
dist x y < c ↔ nndist x y < c := | |
iff.rfl | |
@[simp, norm_cast] lemma dist_le_coe {x y : α} {c : ℝ≥0} : | |
dist x y ≤ c ↔ nndist x y ≤ c := | |
iff.rfl | |
@[simp] lemma edist_lt_of_real {x y : α} {r : ℝ} : edist x y < ennreal.of_real r ↔ dist x y < r := | |
by rw [edist_dist, ennreal.of_real_lt_of_real_iff_of_nonneg dist_nonneg] | |
@[simp] lemma edist_le_of_real {x y : α} {r : ℝ} (hr : 0 ≤ r) : | |
edist x y ≤ ennreal.of_real r ↔ dist x y ≤ r := | |
by rw [edist_dist, ennreal.of_real_le_of_real_iff hr] | |
/--Express `nndist` in terms of `dist`-/ | |
lemma nndist_dist (x y : α) : nndist x y = real.to_nnreal (dist x y) := | |
by rw [dist_nndist, real.to_nnreal_coe] | |
theorem nndist_comm (x y : α) : nndist x y = nndist y x := | |
by simpa only [dist_nndist, nnreal.coe_eq] using dist_comm x y | |
/--Triangle inequality for the nonnegative distance-/ | |
theorem nndist_triangle (x y z : α) : nndist x z ≤ nndist x y + nndist y z := | |
dist_triangle _ _ _ | |
theorem nndist_triangle_left (x y z : α) : nndist x y ≤ nndist z x + nndist z y := | |
dist_triangle_left _ _ _ | |
theorem nndist_triangle_right (x y z : α) : nndist x y ≤ nndist x z + nndist y z := | |
dist_triangle_right _ _ _ | |
/--Express `dist` in terms of `edist`-/ | |
lemma dist_edist (x y : α) : dist x y = (edist x y).to_real := | |
by rw [edist_dist, ennreal.to_real_of_real (dist_nonneg)] | |
namespace metric | |
/- instantiate pseudometric space as a topology -/ | |
variables {x y z : α} {δ ε ε₁ ε₂ : ℝ} {s : set α} | |
/-- `ball x ε` is the set of all points `y` with `dist y x < ε` -/ | |
def ball (x : α) (ε : ℝ) : set α := {y | dist y x < ε} | |
@[simp] theorem mem_ball : y ∈ ball x ε ↔ dist y x < ε := iff.rfl | |
theorem mem_ball' : y ∈ ball x ε ↔ dist x y < ε := by rw [dist_comm, mem_ball] | |
theorem pos_of_mem_ball (hy : y ∈ ball x ε) : 0 < ε := | |
dist_nonneg.trans_lt hy | |
theorem mem_ball_self (h : 0 < ε) : x ∈ ball x ε := | |
show dist x x < ε, by rw dist_self; assumption | |
@[simp] lemma nonempty_ball : (ball x ε).nonempty ↔ 0 < ε := | |
⟨λ ⟨x, hx⟩, pos_of_mem_ball hx, λ h, ⟨x, mem_ball_self h⟩⟩ | |
@[simp] lemma ball_eq_empty : ball x ε = ∅ ↔ ε ≤ 0 := | |
by rw [← not_nonempty_iff_eq_empty, nonempty_ball, not_lt] | |
@[simp] lemma ball_zero : ball x 0 = ∅ := | |
by rw [ball_eq_empty] | |
/-- If a point belongs to an open ball, then there is a strictly smaller radius whose ball also | |
contains it. | |
See also `exists_lt_subset_ball`. -/ | |
lemma exists_lt_mem_ball_of_mem_ball (h : x ∈ ball y ε) : ∃ ε' < ε, x ∈ ball y ε' := | |
begin | |
simp only [mem_ball] at h ⊢, | |
exact ⟨(ε + dist x y) / 2, by linarith, by linarith⟩, | |
end | |
lemma ball_eq_ball (ε : ℝ) (x : α) : | |
uniform_space.ball x {p | dist p.2 p.1 < ε} = metric.ball x ε := rfl | |
lemma ball_eq_ball' (ε : ℝ) (x : α) : | |
uniform_space.ball x {p | dist p.1 p.2 < ε} = metric.ball x ε := | |
by { ext, simp [dist_comm, uniform_space.ball] } | |
@[simp] lemma Union_ball_nat (x : α) : (⋃ n : ℕ, ball x n) = univ := | |
Union_eq_univ_iff.2 $ λ y, exists_nat_gt (dist y x) | |
@[simp] lemma Union_ball_nat_succ (x : α) : (⋃ n : ℕ, ball x (n + 1)) = univ := | |
Union_eq_univ_iff.2 $ λ y, (exists_nat_gt (dist y x)).imp $ λ n hn, | |
hn.trans (lt_add_one _) | |
/-- `closed_ball x ε` is the set of all points `y` with `dist y x ≤ ε` -/ | |
def closed_ball (x : α) (ε : ℝ) := {y | dist y x ≤ ε} | |
@[simp] theorem mem_closed_ball : y ∈ closed_ball x ε ↔ dist y x ≤ ε := iff.rfl | |
theorem mem_closed_ball' : y ∈ closed_ball x ε ↔ dist x y ≤ ε := by rw [dist_comm, mem_closed_ball] | |
/-- `sphere x ε` is the set of all points `y` with `dist y x = ε` -/ | |
def sphere (x : α) (ε : ℝ) := {y | dist y x = ε} | |
@[simp] theorem mem_sphere : y ∈ sphere x ε ↔ dist y x = ε := iff.rfl | |
theorem mem_sphere' : y ∈ sphere x ε ↔ dist x y = ε := by rw [dist_comm, mem_sphere] | |
theorem ne_of_mem_sphere (h : y ∈ sphere x ε) (hε : ε ≠ 0) : y ≠ x := | |
by { contrapose! hε, symmetry, simpa [hε] using h } | |
theorem sphere_eq_empty_of_subsingleton [subsingleton α] (hε : ε ≠ 0) : | |
sphere x ε = ∅ := | |
set.eq_empty_iff_forall_not_mem.mpr $ λ y hy, ne_of_mem_sphere hy hε (subsingleton.elim _ _) | |
theorem sphere_is_empty_of_subsingleton [subsingleton α] (hε : ε ≠ 0) : | |
is_empty (sphere x ε) := | |
by simp only [sphere_eq_empty_of_subsingleton hε, set.has_emptyc.emptyc.is_empty α] | |
theorem mem_closed_ball_self (h : 0 ≤ ε) : x ∈ closed_ball x ε := | |
show dist x x ≤ ε, by rw dist_self; assumption | |
@[simp] lemma nonempty_closed_ball : (closed_ball x ε).nonempty ↔ 0 ≤ ε := | |
⟨λ ⟨x, hx⟩, dist_nonneg.trans hx, λ h, ⟨x, mem_closed_ball_self h⟩⟩ | |
@[simp] lemma closed_ball_eq_empty : closed_ball x ε = ∅ ↔ ε < 0 := | |
by rw [← not_nonempty_iff_eq_empty, nonempty_closed_ball, not_le] | |
theorem ball_subset_closed_ball : ball x ε ⊆ closed_ball x ε := | |
assume y (hy : _ < _), le_of_lt hy | |
theorem sphere_subset_closed_ball : sphere x ε ⊆ closed_ball x ε := | |
λ y, le_of_eq | |
lemma closed_ball_disjoint_ball (h : δ + ε ≤ dist x y) : disjoint (closed_ball x δ) (ball y ε) := | |
λ a ha, (h.trans $ dist_triangle_left _ _ _).not_lt $ add_lt_add_of_le_of_lt ha.1 ha.2 | |
lemma ball_disjoint_closed_ball (h : δ + ε ≤ dist x y) : disjoint (ball x δ) (closed_ball y ε) := | |
(closed_ball_disjoint_ball $ by rwa [add_comm, dist_comm]).symm | |
lemma ball_disjoint_ball (h : δ + ε ≤ dist x y) : disjoint (ball x δ) (ball y ε) := | |
(closed_ball_disjoint_ball h).mono_left ball_subset_closed_ball | |
lemma closed_ball_disjoint_closed_ball (h : δ + ε < dist x y) : | |
disjoint (closed_ball x δ) (closed_ball y ε) := | |
λ a ha, h.not_le $ (dist_triangle_left _ _ _).trans $ add_le_add ha.1 ha.2 | |
theorem sphere_disjoint_ball : disjoint (sphere x ε) (ball x ε) := | |
λ y ⟨hy₁, hy₂⟩, absurd hy₁ $ ne_of_lt hy₂ | |
@[simp] theorem ball_union_sphere : ball x ε ∪ sphere x ε = closed_ball x ε := | |
set.ext $ λ y, ( | ℝ _ _ _).symm|
@[simp] theorem sphere_union_ball : sphere x ε ∪ ball x ε = closed_ball x ε := | |
by rw [union_comm, ball_union_sphere] | |
@[simp] theorem closed_ball_diff_sphere : closed_ball x ε \ sphere x ε = ball x ε := | |
by rw [← ball_union_sphere, set.union_diff_cancel_right sphere_disjoint_ball.symm] | |
@[simp] theorem closed_ball_diff_ball : closed_ball x ε \ ball x ε = sphere x ε := | |
by rw [← ball_union_sphere, set.union_diff_cancel_left sphere_disjoint_ball.symm] | |
theorem mem_ball_comm : x ∈ ball y ε ↔ y ∈ ball x ε := | |
by rw [mem_ball', mem_ball] | |
theorem mem_closed_ball_comm : x ∈ closed_ball y ε ↔ y ∈ closed_ball x ε := | |
by rw [mem_closed_ball', mem_closed_ball] | |
theorem mem_sphere_comm : x ∈ sphere y ε ↔ y ∈ sphere x ε := | |
by rw [mem_sphere', mem_sphere] | |
theorem ball_subset_ball (h : ε₁ ≤ ε₂) : ball x ε₁ ⊆ ball x ε₂ := | |
λ y (yx : _ < ε₁), lt_of_lt_of_le yx h | |
lemma ball_subset_ball' (h : ε₁ + dist x y ≤ ε₂) : ball x ε₁ ⊆ ball y ε₂ := | |
λ z hz, calc | |
dist z y ≤ dist z x + dist x y : dist_triangle _ _ _ | |
... < ε₁ + dist x y : add_lt_add_right hz _ | |
... ≤ ε₂ : h | |
theorem closed_ball_subset_closed_ball (h : ε₁ ≤ ε₂) : | |
closed_ball x ε₁ ⊆ closed_ball x ε₂ := | |
λ y (yx : _ ≤ ε₁), le_trans yx h | |
lemma closed_ball_subset_closed_ball' (h : ε₁ + dist x y ≤ ε₂) : | |
closed_ball x ε₁ ⊆ closed_ball y ε₂ := | |
λ z hz, calc | |
dist z y ≤ dist z x + dist x y : dist_triangle _ _ _ | |
... ≤ ε₁ + dist x y : add_le_add_right hz _ | |
... ≤ ε₂ : h | |
theorem closed_ball_subset_ball (h : ε₁ < ε₂) : | |
closed_ball x ε₁ ⊆ ball x ε₂ := | |
λ y (yh : dist y x ≤ ε₁), lt_of_le_of_lt yh h | |
lemma dist_le_add_of_nonempty_closed_ball_inter_closed_ball | |
(h : (closed_ball x ε₁ ∩ closed_ball y ε₂).nonempty) : | |
dist x y ≤ ε₁ + ε₂ := | |
let ⟨z, hz⟩ := h in calc | |
dist x y ≤ dist z x + dist z y : dist_triangle_left _ _ _ | |
... ≤ ε₁ + ε₂ : add_le_add hz.1 hz.2 | |
lemma dist_lt_add_of_nonempty_closed_ball_inter_ball (h : (closed_ball x ε₁ ∩ ball y ε₂).nonempty) : | |
dist x y < ε₁ + ε₂ := | |
let ⟨z, hz⟩ := h in calc | |
dist x y ≤ dist z x + dist z y : dist_triangle_left _ _ _ | |
... < ε₁ + ε₂ : add_lt_add_of_le_of_lt hz.1 hz.2 | |
lemma dist_lt_add_of_nonempty_ball_inter_closed_ball (h : (ball x ε₁ ∩ closed_ball y ε₂).nonempty) : | |
dist x y < ε₁ + ε₂ := | |
begin | |
rw inter_comm at h, | |
rw [add_comm, dist_comm], | |
exact dist_lt_add_of_nonempty_closed_ball_inter_ball h | |
end | |
lemma dist_lt_add_of_nonempty_ball_inter_ball (h : (ball x ε₁ ∩ ball y ε₂).nonempty) : | |
dist x y < ε₁ + ε₂ := | |
dist_lt_add_of_nonempty_closed_ball_inter_ball $ | |
h.mono (inter_subset_inter ball_subset_closed_ball subset.rfl) | |
@[simp] lemma Union_closed_ball_nat (x : α) : (⋃ n : ℕ, closed_ball x n) = univ := | |
Union_eq_univ_iff.2 $ λ y, exists_nat_ge (dist y x) | |
lemma Union_inter_closed_ball_nat (s : set α) (x : α) : | |
(⋃ (n : ℕ), s ∩ closed_ball x n) = s := | |
by rw [← inter_Union, Union_closed_ball_nat, inter_univ] | |
theorem ball_subset (h : dist x y ≤ ε₂ - ε₁) : ball x ε₁ ⊆ ball y ε₂ := | |
λ z zx, by rw ← add_sub_cancel'_right ε₁ ε₂; exact | |
lt_of_le_of_lt (dist_triangle z x y) (add_lt_add_of_lt_of_le zx h) | |
theorem ball_half_subset (y) (h : y ∈ ball x (ε / 2)) : ball y (ε / 2) ⊆ ball x ε := | |
ball_subset $ by rw sub_self_div_two; exact le_of_lt h | |
theorem exists_ball_subset_ball (h : y ∈ ball x ε) : ∃ ε' > 0, ball y ε' ⊆ ball x ε := | |
⟨_, sub_pos.2 h, ball_subset $ by rw sub_sub_self⟩ | |
/-- If a property holds for all points in closed balls of arbitrarily large radii, then it holds for | |
all points. -/ | |
lemma forall_of_forall_mem_closed_ball (p : α → Prop) (x : α) | |
(H : ∃ᶠ (R : ℝ) in at_top, ∀ y ∈ closed_ball x R, p y) (y : α) : | |
p y := | |
begin | |
obtain ⟨R, hR, h⟩ : ∃ (R : ℝ) (H : dist y x ≤ R), ∀ (z : α), z ∈ closed_ball x R → p z := | |
frequently_iff.1 H (Ici_mem_at_top (dist y x)), | |
exact h _ hR | |
end | |
/-- If a property holds for all points in balls of arbitrarily large radii, then it holds for all | |
points. -/ | |
lemma forall_of_forall_mem_ball (p : α → Prop) (x : α) | |
(H : ∃ᶠ (R : ℝ) in at_top, ∀ y ∈ ball x R, p y) (y : α) : | |
p y := | |
begin | |
obtain ⟨R, hR, h⟩ : ∃ (R : ℝ) (H : dist y x < R), ∀ (z : α), z ∈ ball x R → p z := | |
frequently_iff.1 H (Ioi_mem_at_top (dist y x)), | |
exact h _ hR | |
end | |
theorem is_bounded_iff {s : set α} : | |
is_bounded s ↔ ∃ C : ℝ, ∀ ⦃x⦄, x ∈ s → ∀ ⦃y⦄, y ∈ s → dist x y ≤ C := | |
by rw [is_bounded_def, ← filter.mem_sets, ( | .cobounded_sets α _).out,|
mem_set_of_eq, compl_compl] | |
theorem is_bounded_iff_eventually {s : set α} : | |
is_bounded s ↔ ∀ᶠ C in at_top, ∀ ⦃x⦄, x ∈ s → ∀ ⦃y⦄, y ∈ s → dist x y ≤ C := | |
is_bounded_iff.trans ⟨λ ⟨C, h⟩, eventually_at_top.2 ⟨C, λ C' hC' x hx y hy, (h hx hy).trans hC'⟩, | |
eventually.exists⟩ | |
theorem is_bounded_iff_exists_ge {s : set α} (c : ℝ) : | |
is_bounded s ↔ ∃ C, c ≤ C ∧ ∀ ⦃x⦄, x ∈ s → ∀ ⦃y⦄, y ∈ s → dist x y ≤ C := | |
⟨λ h, ((eventually_ge_at_top c).and (is_bounded_iff_eventually.1 h)).exists, | |
λ h, is_bounded_iff.2 $ h.imp $ λ _, and.right⟩ | |
theorem is_bounded_iff_nndist {s : set α} : | |
is_bounded s ↔ ∃ C : ℝ≥0, ∀ ⦃x⦄, x ∈ s → ∀ ⦃y⦄, y ∈ s → nndist x y ≤ C := | |
by simp only [is_bounded_iff_exists_ge 0, nnreal.exists, ← nnreal.coe_le_coe, ← dist_nndist, | |
nnreal.coe_mk, exists_prop] | |
theorem uniformity_basis_dist : | |
(𝓤 α).has_basis (λ ε : ℝ, 0 < ε) (λ ε, {p:α×α | dist p.1 p.2 < ε}) := | |
begin | |
rw ← pseudo_metric_space.uniformity_dist.symm, | |
refine has_basis_binfi_principal _ nonempty_Ioi, | |
exact λ r (hr : 0 < r) p (hp : 0 < p), ⟨min r p, lt_min hr hp, | |
λ x (hx : dist _ _ < _), lt_of_lt_of_le hx (min_le_left r p), | |
λ x (hx : dist _ _ < _), lt_of_lt_of_le hx (min_le_right r p)⟩ | |
end | |
/-- Given `f : β → ℝ`, if `f` sends `{i | p i}` to a set of positive numbers | |
accumulating to zero, then `f i`-neighborhoods of the diagonal form a basis of `𝓤 α`. | |
For specific bases see `uniformity_basis_dist`, `uniformity_basis_dist_inv_nat_succ`, | |
and `uniformity_basis_dist_inv_nat_pos`. -/ | |
protected theorem mk_uniformity_basis {β : Type*} {p : β → Prop} {f : β → ℝ} | |
(hf₀ : ∀ i, p i → 0 < f i) (hf : ∀ ⦃ε⦄, 0 < ε → ∃ i (hi : p i), f i ≤ ε) : | |
(𝓤 α).has_basis p (λ i, {p:α×α | dist p.1 p.2 < f i}) := | |
begin | |
refine ⟨λ s, uniformity_basis_dist.mem_iff.trans _⟩, | |
split, | |
{ rintros ⟨ε, ε₀, hε⟩, | |
obtain ⟨i, hi, H⟩ : ∃ i (hi : p i), f i ≤ ε, from hf ε₀, | |
exact ⟨i, hi, λ x (hx : _ < _), hε $ lt_of_lt_of_le hx H⟩ }, | |
{ exact λ ⟨i, hi, H⟩, ⟨f i, hf₀ i hi, H⟩ } | |
end | |
theorem uniformity_basis_dist_inv_nat_succ : | |
(𝓤 α).has_basis (λ _, true) (λ n:ℕ, {p:α×α | dist p.1 p.2 < 1 / (↑n+1) }) := | |
metric.mk_uniformity_basis (λ n _, div_pos zero_lt_one $ nat.cast_add_one_pos n) | |
(λ ε ε0, (exists_nat_one_div_lt ε0).imp $ λ n hn, ⟨trivial, le_of_lt hn⟩) | |
theorem uniformity_basis_dist_inv_nat_pos : | |
(𝓤 α).has_basis (λ n:ℕ, 0<n) (λ n:ℕ, {p:α×α | dist p.1 p.2 < 1 / ↑n }) := | |
metric.mk_uniformity_basis (λ n hn, div_pos zero_lt_one $ nat.cast_pos.2 hn) | |
(λ ε ε0, let ⟨n, hn⟩ := exists_nat_one_div_lt ε0 in ⟨n+1, nat.succ_pos n, | |
by exact_mod_cast hn.le⟩) | |
theorem uniformity_basis_dist_pow {r : ℝ} (h0 : 0 < r) (h1 : r < 1) : | |
(𝓤 α).has_basis (λ n:ℕ, true) (λ n:ℕ, {p:α×α | dist p.1 p.2 < r ^ n }) := | |
metric.mk_uniformity_basis (λ n hn, pow_pos h0 _) | |
(λ ε ε0, let ⟨n, hn⟩ := exists_pow_lt_of_lt_one ε0 h1 in ⟨n, trivial, hn.le⟩) | |
theorem uniformity_basis_dist_lt {R : ℝ} (hR : 0 < R) : | |
(𝓤 α).has_basis (λ r : ℝ, 0 < r ∧ r < R) (λ r, {p : α × α | dist p.1 p.2 < r}) := | |
metric.mk_uniformity_basis (λ r, and.left) $ λ r hr, | |
⟨min r (R / 2), ⟨lt_min hr (half_pos hR), min_lt_iff.2 $ or.inr (half_lt_self hR)⟩, | |
min_le_left _ _⟩ | |
/-- Given `f : β → ℝ`, if `f` sends `{i | p i}` to a set of positive numbers | |
accumulating to zero, then closed neighborhoods of the diagonal of sizes `{f i | p i}` | |
form a basis of `𝓤 α`. | |
Currently we have only one specific basis `uniformity_basis_dist_le` based on this constructor. | |
More can be easily added if needed in the future. -/ | |
protected theorem mk_uniformity_basis_le {β : Type*} {p : β → Prop} {f : β → ℝ} | |
(hf₀ : ∀ x, p x → 0 < f x) (hf : ∀ ε, 0 < ε → ∃ x (hx : p x), f x ≤ ε) : | |
(𝓤 α).has_basis p (λ x, {p:α×α | dist p.1 p.2 ≤ f x}) := | |
begin | |
refine ⟨λ s, uniformity_basis_dist.mem_iff.trans _⟩, | |
split, | |
{ rintros ⟨ε, ε₀, hε⟩, | |
rcases exists_between ε₀ with ⟨ε', hε'⟩, | |
rcases hf ε' hε'.1 with ⟨i, hi, H⟩, | |
exact ⟨i, hi, λ x (hx : _ ≤ _), hε $ lt_of_le_of_lt (le_trans hx H) hε'.2⟩ }, | |
{ exact λ ⟨i, hi, H⟩, ⟨f i, hf₀ i hi, λ x (hx : _ < _), H (le_of_lt hx)⟩ } | |
end | |
/-- Contant size closed neighborhoods of the diagonal form a basis | |
of the uniformity filter. -/ | |
theorem uniformity_basis_dist_le : | |
(𝓤 α).has_basis (λ ε : ℝ, 0 < ε) (λ ε, {p:α×α | dist p.1 p.2 ≤ ε}) := | |
metric.mk_uniformity_basis_le (λ _, id) (λ ε ε₀, ⟨ε, ε₀, le_refl ε⟩) | |
theorem uniformity_basis_dist_le_pow {r : ℝ} (h0 : 0 < r) (h1 : r < 1) : | |
(𝓤 α).has_basis (λ n:ℕ, true) (λ n:ℕ, {p:α×α | dist p.1 p.2 ≤ r ^ n }) := | |
metric.mk_uniformity_basis_le (λ n hn, pow_pos h0 _) | |
(λ ε ε0, let ⟨n, hn⟩ := exists_pow_lt_of_lt_one ε0 h1 in ⟨n, trivial, hn.le⟩) | |
theorem mem_uniformity_dist {s : set (α×α)} : | |
s ∈ 𝓤 α ↔ (∃ε>0, ∀{a b:α}, dist a b < ε → (a, b) ∈ s) := | |
uniformity_basis_dist.mem_uniformity_iff | |
/-- A constant size neighborhood of the diagonal is an entourage. -/ | |
theorem dist_mem_uniformity {ε:ℝ} (ε0 : 0 < ε) : | |
{p:α×α | dist p.1 p.2 < ε} ∈ 𝓤 α := | |
mem_uniformity_dist.2 ⟨ε, ε0, λ a b, id⟩ | |
theorem uniform_continuous_iff [pseudo_metric_space β] {f : α → β} : | |
uniform_continuous f ↔ ∀ ε > 0, ∃ δ > 0, | |
∀{a b:α}, dist a b < δ → dist (f a) (f b) < ε := | |
uniformity_basis_dist.uniform_continuous_iff uniformity_basis_dist | |
lemma uniform_continuous_on_iff [pseudo_metric_space β] {f : α → β} {s : set α} : | |
uniform_continuous_on f s ↔ ∀ ε > 0, ∃ δ > 0, ∀ x y ∈ s, dist x y < δ → dist (f x) (f y) < ε := | |
metric.uniformity_basis_dist.uniform_continuous_on_iff metric.uniformity_basis_dist | |
lemma uniform_continuous_on_iff_le [pseudo_metric_space β] {f : α → β} {s : set α} : | |
uniform_continuous_on f s ↔ ∀ ε > 0, ∃ δ > 0, ∀ x y ∈ s, dist x y ≤ δ → dist (f x) (f y) ≤ ε := | |
metric.uniformity_basis_dist_le.uniform_continuous_on_iff metric.uniformity_basis_dist_le | |
theorem uniform_embedding_iff [pseudo_metric_space β] {f : α → β} : | |
uniform_embedding f ↔ function.injective f ∧ uniform_continuous f ∧ | |
∀ δ > 0, ∃ ε > 0, ∀ {a b : α}, dist (f a) (f b) < ε → dist a b < δ := | |
uniform_embedding_def'.trans $ and_congr iff.rfl $ and_congr iff.rfl | |
⟨λ H δ δ0, let ⟨t, tu, ht⟩ := H _ (dist_mem_uniformity δ0), | |
⟨ε, ε0, hε⟩ := mem_uniformity_dist.1 tu in | |
⟨ε, ε0, λ a b h, ht _ _ (hε h)⟩, | |
λ H s su, let ⟨δ, δ0, hδ⟩ := mem_uniformity_dist.1 su, ⟨ε, ε0, hε⟩ := H _ δ0 in | |
⟨_, dist_mem_uniformity ε0, λ a b h, hδ (hε h)⟩⟩ | |
/-- If a map between pseudometric spaces is a uniform embedding then the distance between `f x` | |
and `f y` is controlled in terms of the distance between `x` and `y`. -/ | |
theorem controlled_of_uniform_embedding [pseudo_metric_space β] {f : α → β} : | |
uniform_embedding f → | |
(∀ ε > 0, ∃ δ > 0, ∀ {a b : α}, dist a b < δ → dist (f a) (f b) < ε) ∧ | |
(∀ δ > 0, ∃ ε > 0, ∀ {a b : α}, dist (f a) (f b) < ε → dist a b < δ) := | |
begin | |
assume h, | |
exact ⟨uniform_continuous_iff.1 (uniform_embedding_iff.1 h).2.1, (uniform_embedding_iff.1 h).2.2⟩ | |
end | |
theorem totally_bounded_iff {s : set α} : | |
totally_bounded s ↔ ∀ ε > 0, ∃t : set α, t.finite ∧ s ⊆ ⋃y∈t, ball y ε := | |
⟨λ H ε ε0, H _ (dist_mem_uniformity ε0), | |
λ H r ru, let ⟨ε, ε0, hε⟩ := mem_uniformity_dist.1 ru, | |
⟨t, ft, h⟩ := H ε ε0 in | |
⟨t, ft, h.trans $ Union₂_mono $ λ y yt z, hε⟩⟩ | |
/-- A pseudometric space is totally bounded if one can reconstruct up to any ε>0 any element of the | |
space from finitely many data. -/ | |
lemma totally_bounded_of_finite_discretization {s : set α} | |
(H : ∀ε > (0 : ℝ), ∃ (β : Type u) (_ : fintype β) (F : s → β), | |
∀x y, F x = F y → dist (x:α) y < ε) : | |
totally_bounded s := | |
begin | |
cases s.eq_empty_or_nonempty with hs hs, | |
{ rw hs, exact totally_bounded_empty }, | |
rcases hs with ⟨x0, hx0⟩, | |
haveI : inhabited s := ⟨⟨x0, hx0⟩⟩, | |
refine totally_bounded_iff.2 (λ ε ε0, _), | |
rcases H ε ε0 with ⟨β, fβ, F, hF⟩, | |
resetI, | |
let Finv := function.inv_fun F, | |
refine ⟨range (subtype.val ∘ Finv), finite_range _, λ x xs, _⟩, | |
let x' := Finv (F ⟨x, xs⟩), | |
have : F x' = F ⟨x, xs⟩ := function.inv_fun_eq ⟨⟨x, xs⟩, rfl⟩, | |
simp only [set.mem_Union, set.mem_range], | |
exact ⟨_, ⟨F ⟨x, xs⟩, rfl⟩, hF _ _ this.symm⟩ | |
end | |
theorem finite_approx_of_totally_bounded {s : set α} (hs : totally_bounded s) : | |
∀ ε > 0, ∃ t ⊆ s, set.finite t ∧ s ⊆ ⋃y∈t, ball y ε := | |
begin | |
intros ε ε_pos, | |
rw totally_bounded_iff_subset at hs, | |
exact hs _ (dist_mem_uniformity ε_pos), | |
end | |
/-- Expressing locally uniform convergence on a set using `dist`. -/ | |
lemma tendsto_locally_uniformly_on_iff {ι : Type*} [topological_space β] | |
{F : ι → β → α} {f : β → α} {p : filter ι} {s : set β} : | |
tendsto_locally_uniformly_on F f p s ↔ | |
∀ ε > 0, ∀ x ∈ s, ∃ t ∈ 𝓝[s] x, ∀ᶠ n in p, ∀ y ∈ t, dist (f y) (F n y) < ε := | |
begin | |
refine ⟨λ H ε hε, H _ (dist_mem_uniformity hε), λ H u hu x hx, _⟩, | |
rcases mem_uniformity_dist.1 hu with ⟨ε, εpos, hε⟩, | |
rcases H ε εpos x hx with ⟨t, ht, Ht⟩, | |
exact ⟨t, ht, Ht.mono (λ n hs x hx, hε (hs x hx))⟩ | |
end | |
/-- Expressing uniform convergence on a set using `dist`. -/ | |
lemma tendsto_uniformly_on_iff {ι : Type*} | |
{F : ι → β → α} {f : β → α} {p : filter ι} {s : set β} : | |
tendsto_uniformly_on F f p s ↔ ∀ ε > 0, ∀ᶠ n in p, ∀ x ∈ s, dist (f x) (F n x) < ε := | |
begin | |
refine ⟨λ H ε hε, H _ (dist_mem_uniformity hε), λ H u hu, _⟩, | |
rcases mem_uniformity_dist.1 hu with ⟨ε, εpos, hε⟩, | |
exact (H ε εpos).mono (λ n hs x hx, hε (hs x hx)) | |
end | |
/-- Expressing locally uniform convergence using `dist`. -/ | |
lemma tendsto_locally_uniformly_iff {ι : Type*} [topological_space β] | |
{F : ι → β → α} {f : β → α} {p : filter ι} : | |
tendsto_locally_uniformly F f p ↔ | |
∀ ε > 0, ∀ (x : β), ∃ t ∈ 𝓝 x, ∀ᶠ n in p, ∀ y ∈ t, dist (f y) (F n y) < ε := | |
by simp only [← tendsto_locally_uniformly_on_univ, tendsto_locally_uniformly_on_iff, | |
nhds_within_univ, mem_univ, forall_const, exists_prop] | |
/-- Expressing uniform convergence using `dist`. -/ | |
lemma tendsto_uniformly_iff {ι : Type*} | |
{F : ι → β → α} {f : β → α} {p : filter ι} : | |
tendsto_uniformly F f p ↔ ∀ ε > 0, ∀ᶠ n in p, ∀ x, dist (f x) (F n x) < ε := | |
by { rw [← tendsto_uniformly_on_univ, tendsto_uniformly_on_iff], simp } | |
protected lemma cauchy_iff {f : filter α} : | |
cauchy f ↔ ne_bot f ∧ ∀ ε > 0, ∃ t ∈ f, ∀ x y ∈ t, dist x y < ε := | |
uniformity_basis_dist.cauchy_iff | |
theorem nhds_basis_ball : (𝓝 x).has_basis (λ ε:ℝ, 0 < ε) (ball x) := | |
nhds_basis_uniformity uniformity_basis_dist | |
theorem mem_nhds_iff : s ∈ 𝓝 x ↔ ∃ε>0, ball x ε ⊆ s := | |
nhds_basis_ball.mem_iff | |
theorem eventually_nhds_iff {p : α → Prop} : | |
(∀ᶠ y in 𝓝 x, p y) ↔ ∃ε>0, ∀ ⦃y⦄, dist y x < ε → p y := | |
mem_nhds_iff | |
lemma eventually_nhds_iff_ball {p : α → Prop} : | |
(∀ᶠ y in 𝓝 x, p y) ↔ ∃ ε>0, ∀ y ∈ ball x ε, p y := | |
mem_nhds_iff | |
theorem nhds_basis_closed_ball : (𝓝 x).has_basis (λ ε:ℝ, 0 < ε) (closed_ball x) := | |
nhds_basis_uniformity uniformity_basis_dist_le | |
theorem nhds_basis_ball_inv_nat_succ : | |
(𝓝 x).has_basis (λ _, true) (λ n:ℕ, ball x (1 / (↑n+1))) := | |
nhds_basis_uniformity uniformity_basis_dist_inv_nat_succ | |
theorem nhds_basis_ball_inv_nat_pos : | |
(𝓝 x).has_basis (λ n, 0<n) (λ n:ℕ, ball x (1 / ↑n)) := | |
nhds_basis_uniformity uniformity_basis_dist_inv_nat_pos | |
theorem nhds_basis_ball_pow {r : ℝ} (h0 : 0 < r) (h1 : r < 1) : | |
(𝓝 x).has_basis (λ n, true) (λ n:ℕ, ball x (r ^ n)) := | |
nhds_basis_uniformity (uniformity_basis_dist_pow h0 h1) | |
theorem nhds_basis_closed_ball_pow {r : ℝ} (h0 : 0 < r) (h1 : r < 1) : | |
(𝓝 x).has_basis (λ n, true) (λ n:ℕ, closed_ball x (r ^ n)) := | |
nhds_basis_uniformity (uniformity_basis_dist_le_pow h0 h1) | |
theorem is_open_iff : is_open s ↔ ∀x∈s, ∃ε>0, ball x ε ⊆ s := | |
by simp only [is_open_iff_mem_nhds, mem_nhds_iff] | |
theorem is_open_ball : is_open (ball x ε) := | |
is_open_iff.2 $ λ y, exists_ball_subset_ball | |
theorem ball_mem_nhds (x : α) {ε : ℝ} (ε0 : 0 < ε) : ball x ε ∈ 𝓝 x := | |
is_open_ball.mem_nhds (mem_ball_self ε0) | |
theorem closed_ball_mem_nhds (x : α) {ε : ℝ} (ε0 : 0 < ε) : closed_ball x ε ∈ 𝓝 x := | |
mem_of_superset (ball_mem_nhds x ε0) ball_subset_closed_ball | |
theorem closed_ball_mem_nhds_of_mem {x c : α} {ε : ℝ} (h : x ∈ ball c ε) : | |
closed_ball c ε ∈ 𝓝 x := | |
mem_of_superset (is_open_ball.mem_nhds h) ball_subset_closed_ball | |
theorem nhds_within_basis_ball {s : set α} : | |
(𝓝[s] x).has_basis (λ ε:ℝ, 0 < ε) (λ ε, ball x ε ∩ s) := | |
nhds_within_has_basis nhds_basis_ball s | |
theorem mem_nhds_within_iff {t : set α} : s ∈ 𝓝[t] x ↔ ∃ε>0, ball x ε ∩ t ⊆ s := | |
nhds_within_basis_ball.mem_iff | |
theorem tendsto_nhds_within_nhds_within [pseudo_metric_space β] {t : set β} {f : α → β} {a b} : | |
tendsto f (𝓝[s] a) (𝓝[t] b) ↔ | |
∀ ε > 0, ∃ δ > 0, ∀{x:α}, x ∈ s → dist x a < δ → f x ∈ t ∧ dist (f x) b < ε := | |
(nhds_within_basis_ball.tendsto_iff nhds_within_basis_ball).trans $ | |
forall₂_congr $ λ ε hε, exists₂_congr $ λ δ hδ, | |
forall_congr $ λ x, by simp; itauto | |
theorem tendsto_nhds_within_nhds [pseudo_metric_space β] {f : α → β} {a b} : | |
tendsto f (𝓝[s] a) (𝓝 b) ↔ | |
∀ ε > 0, ∃ δ > 0, ∀{x:α}, x ∈ s → dist x a < δ → dist (f x) b < ε := | |
by { rw [← nhds_within_univ b, tendsto_nhds_within_nhds_within], | |
simp only [mem_univ, true_and] } | |
theorem tendsto_nhds_nhds [pseudo_metric_space β] {f : α → β} {a b} : | |
tendsto f (𝓝 a) (𝓝 b) ↔ | |
∀ ε > 0, ∃ δ > 0, ∀{x:α}, dist x a < δ → dist (f x) b < ε := | |
nhds_basis_ball.tendsto_iff nhds_basis_ball | |
theorem continuous_at_iff [pseudo_metric_space β] {f : α → β} {a : α} : | |
continuous_at f a ↔ | |
∀ ε > 0, ∃ δ > 0, ∀{x:α}, dist x a < δ → dist (f x) (f a) < ε := | |
by rw [continuous_at, tendsto_nhds_nhds] | |
theorem continuous_within_at_iff [pseudo_metric_space β] {f : α → β} {a : α} {s : set α} : | |
continuous_within_at f s a ↔ | |
∀ ε > 0, ∃ δ > 0, ∀{x:α}, x ∈ s → dist x a < δ → dist (f x) (f a) < ε := | |
by rw [continuous_within_at, tendsto_nhds_within_nhds] | |
theorem continuous_on_iff [pseudo_metric_space β] {f : α → β} {s : set α} : | |
continuous_on f s ↔ | |
∀ (b ∈ s) (ε > 0), ∃ δ > 0, ∀a ∈ s, dist a b < δ → dist (f a) (f b) < ε := | |
by simp [continuous_on, continuous_within_at_iff] | |
theorem continuous_iff [pseudo_metric_space β] {f : α → β} : | |
continuous f ↔ | |
∀b (ε > 0), ∃ δ > 0, ∀a, dist a b < δ → dist (f a) (f b) < ε := | |
continuous_iff_continuous_at.trans $ forall_congr $ λ b, tendsto_nhds_nhds | |
theorem tendsto_nhds {f : filter β} {u : β → α} {a : α} : | |
tendsto u f (𝓝 a) ↔ ∀ ε > 0, ∀ᶠ x in f, dist (u x) a < ε := | |
nhds_basis_ball.tendsto_right_iff | |
theorem continuous_at_iff' [topological_space β] {f : β → α} {b : β} : | |
continuous_at f b ↔ | |
∀ ε > 0, ∀ᶠ x in 𝓝 b, dist (f x) (f b) < ε := | |
by rw [continuous_at, tendsto_nhds] | |
theorem continuous_within_at_iff' [topological_space β] {f : β → α} {b : β} {s : set β} : | |
continuous_within_at f s b ↔ | |
∀ ε > 0, ∀ᶠ x in 𝓝[s] b, dist (f x) (f b) < ε := | |
by rw [continuous_within_at, tendsto_nhds] | |
theorem continuous_on_iff' [topological_space β] {f : β → α} {s : set β} : | |
continuous_on f s ↔ | |
∀ (b ∈ s) (ε > 0), ∀ᶠ x in 𝓝[s] b, dist (f x) (f b) < ε := | |
by simp [continuous_on, continuous_within_at_iff'] | |
theorem continuous_iff' [topological_space β] {f : β → α} : | |
continuous f ↔ ∀a (ε > 0), ∀ᶠ x in 𝓝 a, dist (f x) (f a) < ε := | |
continuous_iff_continuous_at.trans $ forall_congr $ λ b, tendsto_nhds | |
theorem tendsto_at_top [nonempty β] [semilattice_sup β] {u : β → α} {a : α} : | |
tendsto u at_top (𝓝 a) ↔ ∀ε>0, ∃N, ∀n≥N, dist (u n) a < ε := | |
(at_top_basis.tendsto_iff nhds_basis_ball).trans $ | |
by { simp only [exists_prop, true_and], refl } | |
/-- | |
A variant of `tendsto_at_top` that | |
uses `∃ N, ∀ n > N, ...` rather than `∃ N, ∀ n ≥ N, ...` | |
-/ | |
theorem tendsto_at_top' [nonempty β] [semilattice_sup β] [no_max_order β] {u : β → α} {a : α} : | |
tendsto u at_top (𝓝 a) ↔ ∀ε>0, ∃N, ∀n>N, dist (u n) a < ε := | |
(at_top_basis_Ioi.tendsto_iff nhds_basis_ball).trans $ | |
by { simp only [exists_prop, true_and], refl } | |
lemma is_open_singleton_iff {α : Type*} [pseudo_metric_space α] {x : α} : | |
is_open ({x} : set α) ↔ ∃ ε > 0, ∀ y, dist y x < ε → y = x := | |
by simp [is_open_iff, subset_singleton_iff, mem_ball] | |
/-- Given a point `x` in a discrete subset `s` of a pseudometric space, there is an open ball | |
centered at `x` and intersecting `s` only at `x`. -/ | |
lemma exists_ball_inter_eq_singleton_of_mem_discrete [discrete_topology s] {x : α} (hx : x ∈ s) : | |
∃ ε > 0, metric.ball x ε ∩ s = {x} := | |
nhds_basis_ball.exists_inter_eq_singleton_of_mem_discrete hx | |
/-- Given a point `x` in a discrete subset `s` of a pseudometric space, there is a closed ball | |
of positive radius centered at `x` and intersecting `s` only at `x`. -/ | |
lemma exists_closed_ball_inter_eq_singleton_of_discrete [discrete_topology s] {x : α} (hx : x ∈ s) : | |
∃ ε > 0, metric.closed_ball x ε ∩ s = {x} := | |
nhds_basis_closed_ball.exists_inter_eq_singleton_of_mem_discrete hx | |
lemma _root_.dense.exists_dist_lt {s : set α} (hs : dense s) (x : α) {ε : ℝ} (hε : 0 < ε) : | |
∃ y ∈ s, dist x y < ε := | |
begin | |
have : (ball x ε).nonempty, by simp [hε], | |
simpa only [mem_ball'] using hs.exists_mem_open is_open_ball this | |
end | |
lemma _root_.dense_range.exists_dist_lt {β : Type*} {f : β → α} (hf : dense_range f) | |
(x : α) {ε : ℝ} (hε : 0 < ε) : | |
∃ y, dist x (f y) < ε := | |
exists_range_iff.1 (hf.exists_dist_lt x hε) | |
end metric | |
open metric | |
/-Instantiate a pseudometric space as a pseudoemetric space. Before we can state the instance, | |
we need to show that the uniform structure coming from the edistance and the | |
distance coincide. -/ | |
/-- Expressing the uniformity in terms of `edist` -/ | |
protected lemma pseudo_metric.uniformity_basis_edist : | |
(𝓤 α).has_basis (λ ε:ℝ≥0∞, 0 < ε) (λ ε, {p | edist p.1 p.2 < ε}) := | |
⟨begin | |
intro t, | |
refine mem_uniformity_dist.trans ⟨_, _⟩; rintro ⟨ε, ε0, Hε⟩, | |
{ use [ennreal.of_real ε, ennreal.of_real_pos.2 ε0], | |
rintros ⟨a, b⟩, | |
simp only [edist_dist, ennreal.of_real_lt_of_real_iff ε0], | |
exact Hε }, | |
{ rcases ennreal.lt_iff_exists_real_btwn.1 ε0 with ⟨ε', _, ε0', hε⟩, | |
rw [ennreal.of_real_pos] at ε0', | |
refine ⟨ε', ε0', λ a b h, Hε (lt_trans _ hε)⟩, | |
rwa [edist_dist, ennreal.of_real_lt_of_real_iff ε0'] } | |
end⟩ | |
theorem metric.uniformity_edist : 𝓤 α = (⨅ ε>0, 𝓟 {p:α×α | edist p.1 p.2 < ε}) := | |
pseudo_metric.uniformity_basis_edist.eq_binfi | |
/-- A pseudometric space induces a pseudoemetric space -/ | |
@[priority 100] -- see Note [lower instance priority] | |
instance pseudo_metric_space.to_pseudo_emetric_space : pseudo_emetric_space α := | |
{ edist := edist, | |
edist_self := by simp [edist_dist], | |
edist_comm := by simp only [edist_dist, dist_comm]; simp, | |
edist_triangle := assume x y z, begin | |
simp only [edist_dist, ← ennreal.of_real_add, dist_nonneg], | |
rw ennreal.of_real_le_of_real_iff _, | |
{ exact dist_triangle _ _ _ }, | |
{ simpa using add_le_add (dist_nonneg : 0 ≤ dist x y) dist_nonneg } | |
end, | |
uniformity_edist := metric.uniformity_edist, | |
..‹pseudo_metric_space α› } | |
/-- In a pseudometric space, an open ball of infinite radius is the whole space -/ | |
lemma metric.eball_top_eq_univ (x : α) : | |
emetric.ball x ∞ = set.univ := | |
set.eq_univ_iff_forall.mpr (λ y, edist_lt_top y x) | |
/-- Balls defined using the distance or the edistance coincide -/ | |
@[simp] lemma metric.emetric_ball {x : α} {ε : ℝ} : emetric.ball x (ennreal.of_real ε) = ball x ε := | |
begin | |
ext y, | |
simp only [emetric.mem_ball, mem_ball, edist_dist], | |
exact ennreal.of_real_lt_of_real_iff_of_nonneg dist_nonneg | |
end | |
/-- Balls defined using the distance or the edistance coincide -/ | |
@[simp] lemma metric.emetric_ball_nnreal {x : α} {ε : ℝ≥0} : emetric.ball x ε = ball x ε := | |
by { convert metric.emetric_ball, simp } | |
/-- Closed balls defined using the distance or the edistance coincide -/ | |
lemma metric.emetric_closed_ball {x : α} {ε : ℝ} (h : 0 ≤ ε) : | |
emetric.closed_ball x (ennreal.of_real ε) = closed_ball x ε := | |
by ext y; simp [edist_dist]; rw ennreal.of_real_le_of_real_iff h | |
/-- Closed balls defined using the distance or the edistance coincide -/ | |
@[simp] lemma metric.emetric_closed_ball_nnreal {x : α} {ε : ℝ≥0} : | |
emetric.closed_ball x ε = closed_ball x ε := | |
by { convert metric.emetric_closed_ball ε.2, simp } | |
@[simp] lemma metric.emetric_ball_top (x : α) : emetric.ball x ⊤ = univ := | |
eq_univ_of_forall $ λ y, edist_lt_top _ _ | |
lemma metric.inseparable_iff {x y : α} : inseparable x y ↔ dist x y = 0 := | |
by rw [emetric.inseparable_iff, edist_nndist, dist_nndist, ennreal.coe_eq_zero, | |
nnreal.coe_eq_zero] | |
/-- Build a new pseudometric space from an old one where the bundled uniform structure is provably | |
(but typically non-definitionaly) equal to some given uniform structure. | |
See Note [forgetful inheritance]. | |
-/ | |
def pseudo_metric_space.replace_uniformity {α} [U : uniform_space α] (m : pseudo_metric_space α) | |
(H : | _ U = _ pseudo_emetric_space.to_uniform_space) :|
pseudo_metric_space α := | |
{ dist := | _ m.to_has_dist,|
dist_self := dist_self, | |
dist_comm := dist_comm, | |
dist_triangle := dist_triangle, | |
edist := edist, | |
edist_dist := edist_dist, | |
to_uniform_space := U, | |
uniformity_dist := H.trans pseudo_metric_space.uniformity_dist } | |
lemma pseudo_metric_space.replace_uniformity_eq {α} [U : uniform_space α] | |
(m : pseudo_metric_space α) | |
(H : | _ U = _ pseudo_emetric_space.to_uniform_space) :|
m.replace_uniformity H = m := | |
by { ext, refl } | |
/-- Build a new pseudo metric space from an old one where the bundled topological structure is | |
provably (but typically non-definitionaly) equal to some given topological structure. | |
See Note [forgetful inheritance]. | |
-/ | |
@[reducible] def pseudo_metric_space.replace_topology {γ} [U : topological_space γ] | |
(m : pseudo_metric_space γ) (H : U = m.to_uniform_space.to_topological_space) : | |
pseudo_metric_space γ := | |
.replace_uniformity γ (m.to_uniform_space.replace_topology H) m rfl | |
lemma pseudo_metric_space.replace_topology_eq {γ} [U : topological_space γ] | |
(m : pseudo_metric_space γ) (H : U = m.to_uniform_space.to_topological_space) : | |
m.replace_topology H = m := | |
by { ext, refl } | |
/-- One gets a pseudometric space from an emetric space if the edistance | |
is everywhere finite, by pushing the edistance to reals. We set it up so that the edist and the | |
uniformity are defeq in the pseudometric space and the pseudoemetric space. In this definition, the | |
distance is given separately, to be able to prescribe some expression which is not defeq to the | |
push-forward of the edistance to reals. -/ | |
def pseudo_emetric_space.to_pseudo_metric_space_of_dist {α : Type u} [e : pseudo_emetric_space α] | |
(dist : α → α → ℝ) | |
(edist_ne_top : ∀x y: α, edist x y ≠ ⊤) | |
(h : ∀x y, dist x y = ennreal.to_real (edist x y)) : | |
pseudo_metric_space α := | |
let m : pseudo_metric_space α := | |
{ dist := dist, | |
dist_self := λx, by simp [h], | |
dist_comm := λx y, by simp [h, pseudo_emetric_space.edist_comm], | |
dist_triangle := λx y z, begin | |
simp only [h], | |
rw [← ennreal.to_real_add (edist_ne_top _ _) (edist_ne_top _ _), | |
ennreal.to_real_le_to_real (edist_ne_top _ _)], | |
{ exact edist_triangle _ _ _ }, | |
{ simp [ennreal.add_eq_top, edist_ne_top] } | |
end, | |
edist := edist, | |
edist_dist := λ x y, by simp [h, ennreal.of_real_to_real, edist_ne_top] } in | |
m.replace_uniformity $ by { rw [uniformity_pseudoedist, metric.uniformity_edist], refl } | |
/-- One gets a pseudometric space from an emetric space if the edistance | |
is everywhere finite, by pushing the edistance to reals. We set it up so that the edist and the | |
uniformity are defeq in the pseudometric space and the emetric space. -/ | |
def pseudo_emetric_space.to_pseudo_metric_space {α : Type u} [e : pseudo_emetric_space α] | |
(h : ∀x y: α, edist x y ≠ ⊤) : pseudo_metric_space α := | |
pseudo_emetric_space.to_pseudo_metric_space_of_dist | |
(λx y, ennreal.to_real (edist x y)) h (λx y, rfl) | |
/-- Build a new pseudometric space from an old one where the bundled bornology structure is provably | |
(but typically non-definitionaly) equal to some given bornology structure. | |
See Note [forgetful inheritance]. | |
-/ | |
def pseudo_metric_space.replace_bornology {α} [B : bornology α] (m : pseudo_metric_space α) | |
(H : ∀ s, | _ B s ↔ _ pseudo_metric_space.to_bornology s) :|
pseudo_metric_space α := | |
{ to_bornology := B, | |
cobounded_sets := set.ext $ compl_surjective.forall.2 $ λ s, (H s).trans $ | |
by rw [is_bounded_iff, mem_set_of_eq, compl_compl], | |
.. m } | |
lemma pseudo_metric_space.replace_bornology_eq {α} [m : pseudo_metric_space α] [B : bornology α] | |
(H : ∀ s, | _ B s ↔ _ pseudo_metric_space.to_bornology s) :|
pseudo_metric_space.replace_bornology _ H = m := | |
by { ext, refl } | |
/-- A very useful criterion to show that a space is complete is to show that all sequences | |
which satisfy a bound of the form `dist (u n) (u m) < B N` for all `n m ≥ N` are | |
converging. This is often applied for `B N = 2^{-N}`, i.e., with a very fast convergence to | |
`0`, which makes it possible to use arguments of converging series, while this is impossible | |
to do in general for arbitrary Cauchy sequences. -/ | |
theorem metric.complete_of_convergent_controlled_sequences (B : ℕ → real) (hB : ∀n, 0 < B n) | |
(H : ∀u : ℕ → α, (∀N n m : ℕ, N ≤ n → N ≤ m → dist (u n) (u m) < B N) → | |
∃x, tendsto u at_top (𝓝 x)) : | |
complete_space α := | |
uniform_space.complete_of_convergent_controlled_sequences | |
(λ n, {p:α×α | dist p.1 p.2 < B n}) (λ n, dist_mem_uniformity $ hB n) H | |
theorem metric.complete_of_cauchy_seq_tendsto : | |
(∀ u : ℕ → α, cauchy_seq u → ∃a, tendsto u at_top (𝓝 a)) → complete_space α := | |
emetric.complete_of_cauchy_seq_tendsto | |
section real | |
/-- Instantiate the reals as a pseudometric space. -/ | |
noncomputable instance real.pseudo_metric_space : pseudo_metric_space ℝ := | |
{ dist := λx y, |x - y|, | |
dist_self := by simp [abs_zero], | |
dist_comm := assume x y, abs_sub_comm _ _, | |
dist_triangle := assume x y z, abs_sub_le _ _ _ } | |
theorem real.dist_eq (x y : ℝ) : dist x y = |x - y| := rfl | |
theorem real.nndist_eq (x y : ℝ) : nndist x y = real.nnabs (x - y) := rfl | |
theorem real.nndist_eq' (x y : ℝ) : nndist x y = real.nnabs (y - x) := nndist_comm _ _ | |
theorem real.dist_0_eq_abs (x : ℝ) : dist x 0 = |x| := | |
by simp [real.dist_eq] | |
theorem real.dist_left_le_of_mem_interval {x y z : ℝ} (h : y ∈ interval x z) : | |
dist x y ≤ dist x z := | |
by simpa only [dist_comm x] using abs_sub_left_of_mem_interval h | |
theorem real.dist_right_le_of_mem_interval {x y z : ℝ} (h : y ∈ interval x z) : | |
dist y z ≤ dist x z := | |
by simpa only [dist_comm _ z] using abs_sub_right_of_mem_interval h | |
theorem real.dist_le_of_mem_interval {x y x' y' : ℝ} (hx : x ∈ interval x' y') | |
(hy : y ∈ interval x' y') : dist x y ≤ dist x' y' := | |
abs_sub_le_of_subinterval $ interval_subset_interval (by rwa interval_swap) (by rwa interval_swap) | |
theorem real.dist_le_of_mem_Icc {x y x' y' : ℝ} (hx : x ∈ Icc x' y') (hy : y ∈ Icc x' y') : | |
dist x y ≤ y' - x' := | |
by simpa only [real.dist_eq, abs_of_nonpos (sub_nonpos.2 $ hx.1.trans hx.2), neg_sub] | |
using real.dist_le_of_mem_interval (Icc_subset_interval hx) (Icc_subset_interval hy) | |
theorem real.dist_le_of_mem_Icc_01 {x y : ℝ} (hx : x ∈ Icc (0:ℝ) 1) (hy : y ∈ Icc (0:ℝ) 1) : | |
dist x y ≤ 1 := | |
by simpa only [sub_zero] using real.dist_le_of_mem_Icc hx hy | |
instance : order_topology ℝ := | |
order_topology_of_nhds_abs $ λ x, | |
by simp only [nhds_basis_ball.eq_binfi, ball, real.dist_eq, abs_sub_comm] | |
lemma real.ball_eq_Ioo (x r : ℝ) : ball x r = Ioo (x - r) (x + r) := | |
set.ext $ λ y, by rw [mem_ball, dist_comm, real.dist_eq, | |
abs_sub_lt_iff, mem_Ioo, ← sub_lt_iff_lt_add', sub_lt] | |
lemma real.closed_ball_eq_Icc {x r : ℝ} : closed_ball x r = Icc (x - r) (x + r) := | |
by ext y; rw [mem_closed_ball, dist_comm, real.dist_eq, | |
abs_sub_le_iff, mem_Icc, ← sub_le_iff_le_add', sub_le] | |
theorem real.Ioo_eq_ball (x y : ℝ) : Ioo x y = ball ((x + y) / 2) ((y - x) / 2) := | |
by rw [real.ball_eq_Ioo, ← sub_div, add_comm, ← sub_add, | |
add_sub_cancel', add_self_div_two, ← add_div, | |
add_assoc, add_sub_cancel'_right, add_self_div_two] | |
theorem real.Icc_eq_closed_ball (x y : ℝ) : Icc x y = closed_ball ((x + y) / 2) ((y - x) / 2) := | |
by rw [real.closed_ball_eq_Icc, ← sub_div, add_comm, ← sub_add, | |
add_sub_cancel', add_self_div_two, ← add_div, | |
add_assoc, add_sub_cancel'_right, add_self_div_two] | |
section metric_ordered | |
variables [preorder α] [compact_Icc_space α] | |
lemma totally_bounded_Icc (a b : α) : totally_bounded (Icc a b) := | |
is_compact_Icc.totally_bounded | |
lemma totally_bounded_Ico (a b : α) : totally_bounded (Ico a b) := | |
totally_bounded_subset Ico_subset_Icc_self (totally_bounded_Icc a b) | |
lemma totally_bounded_Ioc (a b : α) : totally_bounded (Ioc a b) := | |
totally_bounded_subset Ioc_subset_Icc_self (totally_bounded_Icc a b) | |
lemma totally_bounded_Ioo (a b : α) : totally_bounded (Ioo a b) := | |
totally_bounded_subset Ioo_subset_Icc_self (totally_bounded_Icc a b) | |
end metric_ordered | |
/-- Special case of the sandwich theorem; see `tendsto_of_tendsto_of_tendsto_of_le_of_le'` for the | |
general case. -/ | |
lemma squeeze_zero' {α} {f g : α → ℝ} {t₀ : filter α} (hf : ∀ᶠ t in t₀, 0 ≤ f t) | |
(hft : ∀ᶠ t in t₀, f t ≤ g t) (g0 : tendsto g t₀ (nhds 0)) : tendsto f t₀ (𝓝 0) := | |
tendsto_of_tendsto_of_tendsto_of_le_of_le' tendsto_const_nhds g0 hf hft | |
/-- Special case of the sandwich theorem; see `tendsto_of_tendsto_of_tendsto_of_le_of_le` | |
and `tendsto_of_tendsto_of_tendsto_of_le_of_le'` for the general case. -/ | |
lemma squeeze_zero {α} {f g : α → ℝ} {t₀ : filter α} (hf : ∀t, 0 ≤ f t) (hft : ∀t, f t ≤ g t) | |
(g0 : tendsto g t₀ (𝓝 0)) : tendsto f t₀ (𝓝 0) := | |
squeeze_zero' (eventually_of_forall hf) (eventually_of_forall hft) g0 | |
theorem metric.uniformity_eq_comap_nhds_zero : | |
𝓤 α = comap (λp:α×α, dist p.1 p.2) (𝓝 (0 : ℝ)) := | |
by { ext s, | |
simp [mem_uniformity_dist, (nhds_basis_ball.comap _).mem_iff, subset_def, real.dist_0_eq_abs] } | |
lemma cauchy_seq_iff_tendsto_dist_at_top_0 [nonempty β] [semilattice_sup β] {u : β → α} : | |
cauchy_seq u ↔ tendsto (λ (n : β × β), dist (u n.1) (u n.2)) at_top (𝓝 0) := | |
by rw [cauchy_seq_iff_tendsto, metric.uniformity_eq_comap_nhds_zero, tendsto_comap_iff, | |
prod.map_def] | |
lemma tendsto_uniformity_iff_dist_tendsto_zero {ι : Type*} {f : ι → α × α} {p : filter ι} : | |
tendsto f p (𝓤 α) ↔ tendsto (λ x, dist (f x).1 (f x).2) p (𝓝 0) := | |
by rw [metric.uniformity_eq_comap_nhds_zero, tendsto_comap_iff] | |
lemma filter.tendsto.congr_dist {ι : Type*} {f₁ f₂ : ι → α} {p : filter ι} {a : α} | |
(h₁ : tendsto f₁ p (𝓝 a)) (h : tendsto (λ x, dist (f₁ x) (f₂ x)) p (𝓝 0)) : | |
tendsto f₂ p (𝓝 a) := | |
h₁.congr_uniformity $ tendsto_uniformity_iff_dist_tendsto_zero.2 h | |
alias filter.tendsto.congr_dist ← tendsto_of_tendsto_of_dist | |
lemma tendsto_iff_of_dist {ι : Type*} {f₁ f₂ : ι → α} {p : filter ι} {a : α} | |
(h : tendsto (λ x, dist (f₁ x) (f₂ x)) p (𝓝 0)) : | |
tendsto f₁ p (𝓝 a) ↔ tendsto f₂ p (𝓝 a) := | |
uniform.tendsto_congr $ tendsto_uniformity_iff_dist_tendsto_zero.2 h | |
/-- If `u` is a neighborhood of `x`, then for small enough `r`, the closed ball | |
`closed_ball x r` is contained in `u`. -/ | |
lemma eventually_closed_ball_subset {x : α} {u : set α} (hu : u ∈ 𝓝 x) : | |
∀ᶠ r in 𝓝 (0 : ℝ), closed_ball x r ⊆ u := | |
begin | |
obtain ⟨ε, εpos, hε⟩ : ∃ ε (hε : 0 < ε), closed_ball x ε ⊆ u := | |
nhds_basis_closed_ball.mem_iff.1 hu, | |
have : Iic ε ∈ 𝓝 (0 : ℝ) := Iic_mem_nhds εpos, | |
filter_upwards [this] with _ hr using subset.trans (closed_ball_subset_closed_ball hr) hε, | |
end | |
end real | |
section cauchy_seq | |
variables [nonempty β] [semilattice_sup β] | |
/-- In a pseudometric space, Cauchy sequences are characterized by the fact that, eventually, | |
the distance between its elements is arbitrarily small -/ | |
@[nolint ge_or_gt] -- see Note [nolint_ge] | |
theorem metric.cauchy_seq_iff {u : β → α} : | |
cauchy_seq u ↔ ∀ε>0, ∃N, ∀m n≥N, dist (u m) (u n) < ε := | |
uniformity_basis_dist.cauchy_seq_iff | |
/-- A variation around the pseudometric characterization of Cauchy sequences -/ | |
theorem metric.cauchy_seq_iff' {u : β → α} : | |
cauchy_seq u ↔ ∀ε>0, ∃N, ∀n≥N, dist (u n) (u N) < ε := | |
uniformity_basis_dist.cauchy_seq_iff' | |
/-- In a pseudometric space, unifom Cauchy sequences are characterized by the fact that, eventually, | |
the distance between all its elements is uniformly, arbitrarily small -/ | |
@[nolint ge_or_gt] -- see Note [nolint_ge] | |
theorem metric.uniform_cauchy_seq_on_iff {γ : Type*} | |
{F : β → γ → α} {s : set γ} : | |
uniform_cauchy_seq_on F at_top s ↔ | |
∀ ε : ℝ, ε > 0 → ∃ (N : β), ∀ m : β, m ≥ N → ∀ n : β, n ≥ N → ∀ x : γ, x ∈ s → | |
dist (F m x) (F n x) < ε := | |
begin | |
split, | |
{ intros h ε hε, | |
let u := { a : α × α | dist a.fst a.snd < ε }, | |
have hu : u ∈ 𝓤 α := metric.mem_uniformity_dist.mpr ⟨ε, hε, (λ a b, by simp)⟩, | |
rw ← | .eventually_at_top_prod_self' _ _ _|
(λ m, ∀ x : γ, x ∈ s → dist (F m.fst x) (F m.snd x) < ε), | |
specialize h u hu, | |
rw prod_at_top_at_top_eq at h, | |
exact h.mono (λ n h x hx, set.mem_set_of_eq.mp (h x hx)), }, | |
{ intros h u hu, | |
rcases (metric.mem_uniformity_dist.mp hu) with ⟨ε, hε, hab⟩, | |
rcases h ε hε with ⟨N, hN⟩, | |
rw [prod_at_top_at_top_eq, eventually_at_top], | |
use (N, N), | |
intros b hb x hx, | |
rcases hb with ⟨hbl, hbr⟩, | |
exact hab (hN b.fst hbl.ge b.snd hbr.ge x hx), }, | |
end | |
/-- If the distance between `s n` and `s m`, `n ≤ m` is bounded above by `b n` | |
and `b` converges to zero, then `s` is a Cauchy sequence. -/ | |
lemma cauchy_seq_of_le_tendsto_0' {s : β → α} (b : β → ℝ) | |
(h : ∀ n m : β, n ≤ m → dist (s n) (s m) ≤ b n) (h₀ : tendsto b at_top (𝓝 0)) : | |
cauchy_seq s := | |
metric.cauchy_seq_iff'.2 $ λ ε ε0, | |
(h₀.eventually (gt_mem_nhds ε0)).exists.imp $ λ N hN n hn, | |
calc dist (s n) (s N) = dist (s N) (s n) : dist_comm _ _ | |
... ≤ b N : h _ _ hn | |
... < ε : hN | |
/-- If the distance between `s n` and `s m`, `n, m ≥ N` is bounded above by `b N` | |
and `b` converges to zero, then `s` is a Cauchy sequence. -/ | |
lemma cauchy_seq_of_le_tendsto_0 {s : β → α} (b : β → ℝ) | |
(h : ∀ n m N : β, N ≤ n → N ≤ m → dist (s n) (s m) ≤ b N) (h₀ : tendsto b at_top (𝓝 0)) : | |
cauchy_seq s := | |
cauchy_seq_of_le_tendsto_0' b (λ n m hnm, h _ _ _ le_rfl hnm) h₀ | |
/-- A Cauchy sequence on the natural numbers is bounded. -/ | |
theorem cauchy_seq_bdd {u : ℕ → α} (hu : cauchy_seq u) : | |
∃ R > 0, ∀ m n, dist (u m) (u n) < R := | |
begin | |
rcases metric.cauchy_seq_iff'.1 hu 1 zero_lt_one with ⟨N, hN⟩, | |
suffices : ∃ R > 0, ∀ n, dist (u n) (u N) < R, | |
{ rcases this with ⟨R, R0, H⟩, | |
exact ⟨_, add_pos R0 R0, λ m n, | |
lt_of_le_of_lt (dist_triangle_right _ _ _) (add_lt_add (H m) (H n))⟩ }, | |
let R := finset.sup (finset.range N) (λ n, nndist (u n) (u N)), | |
refine ⟨↑R + 1, add_pos_of_nonneg_of_pos R.2 zero_lt_one, λ n, _⟩, | |
cases le_or_lt N n, | |
{ exact lt_of_lt_of_le (hN _ h) (le_add_of_nonneg_left R.2) }, | |
{ have : _ ≤ R := finset.le_sup (finset.mem_range.2 h), | |
exact lt_of_le_of_lt this (lt_add_of_pos_right _ zero_lt_one) } | |
end | |
/-- Yet another metric characterization of Cauchy sequences on integers. This one is often the | |
most efficient. -/ | |
lemma cauchy_seq_iff_le_tendsto_0 {s : ℕ → α} : cauchy_seq s ↔ ∃ b : ℕ → ℝ, | |
(∀ n, 0 ≤ b n) ∧ | |
(∀ n m N : ℕ, N ≤ n → N ≤ m → dist (s n) (s m) ≤ b N) ∧ | |
tendsto b at_top (𝓝 0) := | |
⟨λ hs, begin | |
/- `s` is a Cauchy sequence. The sequence `b` will be constructed by taking | |
the supremum of the distances between `s n` and `s m` for `n m ≥ N`. | |
First, we prove that all these distances are bounded, as otherwise the Sup | |
would not make sense. -/ | |
let S := λ N, (λ(p : ℕ × ℕ), dist (s p.1) (s p.2)) '' {p | p.1 ≥ N ∧ p.2 ≥ N}, | |
have hS : ∀ N, ∃ x, ∀ y ∈ S N, y ≤ x, | |
{ rcases cauchy_seq_bdd hs with ⟨R, R0, hR⟩, | |
refine λ N, ⟨R, _⟩, rintro _ ⟨⟨m, n⟩, _, rfl⟩, | |
exact le_of_lt (hR m n) }, | |
have bdd : bdd_above (range (λ(p : ℕ × ℕ), dist (s p.1) (s p.2))), | |
{ rcases cauchy_seq_bdd hs with ⟨R, R0, hR⟩, | |
use R, rintro _ ⟨⟨m, n⟩, rfl⟩, exact le_of_lt (hR m n) }, | |
-- Prove that it bounds the distances of points in the Cauchy sequence | |
have ub : ∀ m n N, N ≤ m → N ≤ n → dist (s m) (s n) ≤ Sup (S N) := | |
λ m n N hm hn, le_cSup (hS N) ⟨⟨_, _⟩, ⟨hm, hn⟩, rfl⟩, | |
have S0m : ∀ n, (0:ℝ) ∈ S n := λ n, ⟨⟨n, n⟩, ⟨le_rfl, le_rfl⟩, dist_self _⟩, | |
have S0 := λ n, le_cSup (hS n) (S0m n), | |
-- Prove that it tends to `0`, by using the Cauchy property of `s` | |
refine ⟨λ N, Sup (S N), S0, ub, metric.tendsto_at_top.2 (λ ε ε0, _)⟩, | |
refine (metric.cauchy_seq_iff.1 hs (ε/2) (half_pos ε0)).imp (λ N hN n hn, _), | |
rw [real.dist_0_eq_abs, abs_of_nonneg (S0 n)], | |
refine lt_of_le_of_lt (cSup_le ⟨_, S0m _⟩ _) (half_lt_self ε0), | |
rintro _ ⟨⟨m', n'⟩, ⟨hm', hn'⟩, rfl⟩, | |
exact le_of_lt (hN _ (le_trans hn hm') _ (le_trans hn hn')) | |
end, | |
λ ⟨b, _, b_bound, b_lim⟩, cauchy_seq_of_le_tendsto_0 b b_bound b_lim⟩ | |
end cauchy_seq | |
/-- Pseudometric space structure pulled back by a function. -/ | |
def pseudo_metric_space.induced {α β} (f : α → β) | |
(m : pseudo_metric_space β) : pseudo_metric_space α := | |
{ dist := λ x y, dist (f x) (f y), | |
dist_self := λ x, dist_self _, | |
dist_comm := λ x y, dist_comm _ _, | |
dist_triangle := λ x y z, dist_triangle _ _ _, | |
edist := λ x y, edist (f x) (f y), | |
edist_dist := λ x y, edist_dist _ _, | |
to_uniform_space := uniform_space.comap f m.to_uniform_space, | |
uniformity_dist := begin | |
apply | _ _ _ _ _ (λ x y, dist (f x) (f y)),|
refine compl_surjective.forall.2 (λ s, compl_mem_comap.trans $ mem_uniformity_dist.trans _), | |
simp only [mem_compl_iff, | _ (_ ∈ _), ← prod.forall', prod.mk.eta, ball_image_iff]|
end, | |
to_bornology := bornology.induced f, | |
cobounded_sets := set.ext $ compl_surjective.forall.2 $ λ s, | |
by simp only [compl_mem_comap, filter.mem_sets, ← is_bounded_def, mem_set_of_eq, compl_compl, | |
is_bounded_iff, ball_image_iff] } | |
/-- Pull back a pseudometric space structure by an inducing map. This is a version of | |
`pseudo_metric_space.induced` useful in case if the domain already has a `topological_space` | |
structure. -/ | |
def inducing.comap_pseudo_metric_space {α β} [topological_space α] [pseudo_metric_space β] | |
{f : α → β} (hf : inducing f) : pseudo_metric_space α := | |
(pseudo_metric_space.induced f ‹_›).replace_topology hf.induced | |
/-- Pull back a pseudometric space structure by a uniform inducing map. This is a version of | |
`pseudo_metric_space.induced` useful in case if the domain already has a `uniform_space` | |
structure. -/ | |
def uniform_inducing.comap_pseudo_metric_space {α β} [uniform_space α] [pseudo_metric_space β] | |
(f : α → β) (h : uniform_inducing f) : pseudo_metric_space α := | |
(pseudo_metric_space.induced f ‹_›).replace_uniformity h.comap_uniformity.symm | |
instance subtype.pseudo_metric_space {p : α → Prop} : pseudo_metric_space (subtype p) := | |
pseudo_metric_space.induced coe ‹_› | |
theorem subtype.dist_eq {p : α → Prop} (x y : subtype p) : dist x y = dist (x : α) y := rfl | |
theorem subtype.nndist_eq {p : α → Prop} (x y : subtype p) : nndist x y = nndist (x : α) y := rfl | |
namespace mul_opposite | |
@[to_additive] | |
instance : pseudo_metric_space (αᵐᵒᵖ) := pseudo_metric_space.induced mul_opposite.unop ‹_› | |
@[simp, to_additive] theorem dist_unop (x y : αᵐᵒᵖ) : dist (unop x) (unop y) = dist x y := rfl | |
@[simp, to_additive] theorem dist_op (x y : α) : dist (op x) (op y) = dist x y := rfl | |
@[simp, to_additive] theorem nndist_unop (x y : αᵐᵒᵖ) : nndist (unop x) (unop y) = nndist x y := rfl | |
@[simp, to_additive] theorem nndist_op (x y : α) : nndist (op x) (op y) = nndist x y := rfl | |
end mul_opposite | |
section nnreal | |
noncomputable instance : pseudo_metric_space ℝ≥0 := subtype.pseudo_metric_space | |
lemma nnreal.dist_eq (a b : ℝ≥0) : dist a b = |(a:ℝ) - b| := rfl | |
lemma nnreal.nndist_eq (a b : ℝ≥0) : | |
nndist a b = max (a - b) (b - a) := | |
begin | |
/- WLOG, `b ≤ a`. `wlog h : b ≤ a` works too but it is much slower because Lean tries to prove one | |
case from the other and fails; `tactic.skip` tells Lean not to try. -/ | |
wlog h : b ≤ a := le_total b a using [a b, b a] tactic.skip, | |
{ rw [← nnreal.coe_eq, ← dist_nndist, nnreal.dist_eq, tsub_eq_zero_iff_le.2 h, | |
max_eq_left (zero_le $ a - b), ← nnreal.coe_sub h, abs_of_nonneg (a - b).coe_nonneg] }, | |
{ rwa [nndist_comm, max_comm] } | |
end | |
@[simp] lemma nnreal.nndist_zero_eq_val (z : ℝ≥0) : nndist 0 z = z := | |
by simp only [nnreal.nndist_eq, max_eq_right, tsub_zero, zero_tsub, zero_le'] | |
@[simp] lemma nnreal.nndist_zero_eq_val' (z : ℝ≥0) : nndist z 0 = z := | |
by { rw nndist_comm, exact nnreal.nndist_zero_eq_val z, } | |
lemma nnreal.le_add_nndist (a b : ℝ≥0) : a ≤ b + nndist a b := | |
begin | |
suffices : (a : ℝ) ≤ (b : ℝ) + (dist a b), | |
{ exact nnreal.coe_le_coe.mp this, }, | |
linarith [le_of_abs_le (by refl : abs (a-b : ℝ) ≤ (dist a b))], | |
end | |
end nnreal | |
section ulift | |
variables [pseudo_metric_space β] | |
instance : pseudo_metric_space (ulift β) := | |
pseudo_metric_space.induced ulift.down ‹_› | |
lemma ulift.dist_eq (x y : ulift β) : dist x y = dist x.down y.down := rfl | |
lemma ulift.nndist_eq (x y : ulift β) : nndist x y = nndist x.down y.down := rfl | |
@[simp] lemma ulift.dist_up_up (x y : β) : dist (ulift.up x) (ulift.up y) = dist x y := rfl | |
@[simp] lemma ulift.nndist_up_up (x y : β) : nndist (ulift.up x) (ulift.up y) = nndist x y := rfl | |
end ulift | |
section prod | |
variables [pseudo_metric_space β] | |
noncomputable instance prod.pseudo_metric_space_max : | |
pseudo_metric_space (α × β) := | |
(pseudo_emetric_space.to_pseudo_metric_space_of_dist | |
(λ x y : α × β, max (dist x.1 y.1) (dist x.2 y.2)) | |
(λ x y, (max_lt (edist_lt_top _ _) (edist_lt_top _ _)).ne) | |
(λ x y, by simp only [dist_edist, ← ennreal.to_real_max (edist_ne_top _ _) (edist_ne_top _ _), | |
prod.edist_eq])).replace_bornology $ | |
λ s, by { simp only [← is_bounded_image_fst_and_snd, is_bounded_iff_eventually, ball_image_iff, | |
← eventually_and, ← forall_and_distrib, ← max_le_iff], refl } | |
lemma prod.dist_eq {x y : α × β} : | |
dist x y = max (dist x.1 y.1) (dist x.2 y.2) := rfl | |
@[simp] | |
lemma dist_prod_same_left {x : α} {y₁ y₂ : β} : dist (x, y₁) (x, y₂) = dist y₁ y₂ := | |
by simp [prod.dist_eq, dist_nonneg] | |
@[simp] | |
lemma dist_prod_same_right {x₁ x₂ : α} {y : β} : dist (x₁, y) (x₂, y) = dist x₁ x₂ := | |
by simp [prod.dist_eq, dist_nonneg] | |
theorem ball_prod_same (x : α) (y : β) (r : ℝ) : | |
ball x r ×ˢ ball y r = ball (x, y) r := | |
ext $ λ z, by simp [prod.dist_eq] | |
theorem closed_ball_prod_same (x : α) (y : β) (r : ℝ) : | |
closed_ball x r ×ˢ closed_ball y r = closed_ball (x, y) r := | |
ext $ λ z, by simp [prod.dist_eq] | |
end prod | |
theorem uniform_continuous_dist : uniform_continuous (λp:α×α, dist p.1 p.2) := | |
metric.uniform_continuous_iff.2 (λ ε ε0, ⟨ε/2, half_pos ε0, | |
begin | |
suffices, | |
{ intros p q h, cases p with p₁ p₂, cases q with q₁ q₂, | |
cases max_lt_iff.1 h with h₁ h₂, clear h, | |
dsimp at h₁ h₂ ⊢, | |
rw real.dist_eq, | |
refine abs_sub_lt_iff.2 ⟨_, _⟩, | |
{ revert p₁ p₂ q₁ q₂ h₁ h₂, exact this }, | |
{ apply this; rwa dist_comm } }, | |
intros p₁ p₂ q₁ q₂ h₁ h₂, | |
have := add_lt_add | |
(abs_sub_lt_iff.1 (lt_of_le_of_lt (abs_dist_sub_le p₁ q₁ p₂) h₁)).1 | |
(abs_sub_lt_iff.1 (lt_of_le_of_lt (abs_dist_sub_le p₂ q₂ q₁) h₂)).1, | |
rwa [add_halves, dist_comm p₂, sub_add_sub_cancel, dist_comm q₂] at this | |
end⟩) | |
theorem uniform_continuous.dist [uniform_space β] {f g : β → α} | |
(hf : uniform_continuous f) (hg : uniform_continuous g) : | |
uniform_continuous (λb, dist (f b) (g b)) := | |
uniform_continuous_dist.comp (hf.prod_mk hg) | |
@[continuity] | |
theorem continuous_dist : continuous (λp:α×α, dist p.1 p.2) := | |
uniform_continuous_dist.continuous | |
@[continuity] | |
theorem continuous.dist [topological_space β] {f g : β → α} | |
(hf : continuous f) (hg : continuous g) : continuous (λb, dist (f b) (g b)) := | |
continuous_dist.comp (hf.prod_mk hg : _) | |
theorem filter.tendsto.dist {f g : β → α} {x : filter β} {a b : α} | |
(hf : tendsto f x (𝓝 a)) (hg : tendsto g x (𝓝 b)) : | |
tendsto (λx, dist (f x) (g x)) x (𝓝 (dist a b)) := | |
(continuous_dist.tendsto (a, b)).comp (hf.prod_mk_nhds hg) | |
lemma nhds_comap_dist (a : α) : (𝓝 (0 : ℝ)).comap (λa', dist a' a) = 𝓝 a := | |
by simp only [ | α, metric.uniformity_eq_comap_nhds_zero,|
comap_comap, (∘), dist_comm] | |
lemma tendsto_iff_dist_tendsto_zero {f : β → α} {x : filter β} {a : α} : | |
(tendsto f x (𝓝 a)) ↔ (tendsto (λb, dist (f b) a) x (𝓝 0)) := | |
by rw [← nhds_comap_dist a, tendsto_comap_iff] | |
lemma uniform_continuous_nndist : uniform_continuous (λp:α×α, nndist p.1 p.2) := | |
uniform_continuous_subtype_mk uniform_continuous_dist _ | |
lemma uniform_continuous.nndist [uniform_space β] {f g : β → α} (hf : uniform_continuous f) | |
(hg : uniform_continuous g) : | |
uniform_continuous (λ b, nndist (f b) (g b)) := | |
uniform_continuous_nndist.comp (hf.prod_mk hg) | |
lemma continuous_nndist : continuous (λp:α×α, nndist p.1 p.2) := | |
uniform_continuous_nndist.continuous | |
lemma continuous.nndist [topological_space β] {f g : β → α} | |
(hf : continuous f) (hg : continuous g) : continuous (λb, nndist (f b) (g b)) := | |
continuous_nndist.comp (hf.prod_mk hg : _) | |
theorem filter.tendsto.nndist {f g : β → α} {x : filter β} {a b : α} | |
(hf : tendsto f x (𝓝 a)) (hg : tendsto g x (𝓝 b)) : | |
tendsto (λx, nndist (f x) (g x)) x (𝓝 (nndist a b)) := | |
(continuous_nndist.tendsto (a, b)).comp (hf.prod_mk_nhds hg) | |
namespace metric | |
variables {x y z : α} {ε ε₁ ε₂ : ℝ} {s : set α} | |
theorem is_closed_ball : is_closed (closed_ball x ε) := | |
is_closed_le (continuous_id.dist continuous_const) continuous_const | |
lemma is_closed_sphere : is_closed (sphere x ε) := | |
is_closed_eq (continuous_id.dist continuous_const) continuous_const | |
@[simp] theorem closure_closed_ball : closure (closed_ball x ε) = closed_ball x ε := | |
is_closed_ball.closure_eq | |
theorem closure_ball_subset_closed_ball : closure (ball x ε) ⊆ closed_ball x ε := | |
closure_minimal ball_subset_closed_ball is_closed_ball | |
theorem frontier_ball_subset_sphere : frontier (ball x ε) ⊆ sphere x ε := | |
frontier_lt_subset_eq (continuous_id.dist continuous_const) continuous_const | |
theorem frontier_closed_ball_subset_sphere : frontier (closed_ball x ε) ⊆ sphere x ε := | |
frontier_le_subset_eq (continuous_id.dist continuous_const) continuous_const | |
theorem ball_subset_interior_closed_ball : ball x ε ⊆ interior (closed_ball x ε) := | |
interior_maximal ball_subset_closed_ball is_open_ball | |
/-- ε-characterization of the closure in pseudometric spaces-/ | |
theorem mem_closure_iff {s : set α} {a : α} : | |
a ∈ closure s ↔ ∀ε>0, ∃b ∈ s, dist a b < ε := | |
(mem_closure_iff_nhds_basis nhds_basis_ball).trans $ | |
by simp only [mem_ball, dist_comm] | |
lemma mem_closure_range_iff {e : β → α} {a : α} : | |
a ∈ closure (range e) ↔ ∀ε>0, ∃ k : β, dist a (e k) < ε := | |
by simp only [mem_closure_iff, exists_range_iff] | |
lemma mem_closure_range_iff_nat {e : β → α} {a : α} : | |
a ∈ closure (range e) ↔ ∀n : ℕ, ∃ k : β, dist a (e k) < 1 / ((n : ℝ) + 1) := | |
(mem_closure_iff_nhds_basis nhds_basis_ball_inv_nat_succ).trans $ | |
by simp only [mem_ball, dist_comm, exists_range_iff, forall_const] | |
theorem mem_of_closed' {s : set α} (hs : is_closed s) {a : α} : | |
a ∈ s ↔ ∀ε>0, ∃b ∈ s, dist a b < ε := | |
by simpa only [hs.closure_eq] using _ _ s a | |
lemma closed_ball_zero' (x : α) : closed_ball x 0 = closure {x} := | |
subset.antisymm | |
(λ y hy, mem_closure_iff.2 $ λ ε ε0, ⟨x, mem_singleton x, (mem_closed_ball.1 hy).trans_lt ε0⟩) | |
(closure_minimal (singleton_subset_iff.2 (dist_self x).le) is_closed_ball) | |
lemma dense_iff {s : set α} : | |
dense s ↔ ∀ x, ∀ r > 0, (ball x r ∩ s).nonempty := | |
forall_congr $ λ x, by simp only [mem_closure_iff, set.nonempty, exists_prop, mem_inter_eq, | |
mem_ball', and_comm] | |
lemma dense_range_iff {f : β → α} : | |
dense_range f ↔ ∀ x, ∀ r > 0, ∃ y, dist x (f y) < r := | |
forall_congr $ λ x, by simp only [mem_closure_iff, exists_range_iff] | |
/-- If a set `s` is separable, then the corresponding subtype is separable in a metric space. | |
This is not obvious, as the countable set whose closure covers `s` does not need in general to | |
be contained in `s`. -/ | |
lemma _root_.topological_space.is_separable.separable_space {s : set α} (hs : is_separable s) : | |
separable_space s := | |
begin | |
classical, | |
rcases eq_empty_or_nonempty s with rfl|⟨⟨x₀, x₀s⟩⟩, | |
{ haveI : encodable (∅ : set α) := fintype.to_encodable ↥∅, exact encodable.to_separable_space }, | |
rcases hs with ⟨c, hc, h'c⟩, | |
haveI : encodable c := hc.to_encodable, | |
obtain ⟨u, -, u_pos, u_lim⟩ : ∃ (u : ℕ → ℝ), strict_anti u ∧ (∀ (n : ℕ), 0 < u n) ∧ | |
tendsto u at_top (𝓝 0) := exists_seq_strict_anti_tendsto (0 : ℝ), | |
let f : c × ℕ → α := λ p, if h : (metric.ball (p.1 : α) (u p.2) ∩ s).nonempty then h.some else x₀, | |
have fs : ∀ p, f p ∈ s, | |
{ rintros ⟨y, n⟩, | |
by_cases h : (ball (y : α) (u n) ∩ s).nonempty, | |
{ simpa only [f, h, dif_pos] using h.some_spec.2 }, | |
{ simpa only [f, h, not_false_iff, dif_neg] } }, | |
let g : c × ℕ → s := λ p, ⟨f p, fs p⟩, | |
apply separable_space_of_dense_range g, | |
apply metric.dense_range_iff.2, | |
rintros ⟨x, xs⟩ r (rpos : 0 < r), | |
obtain ⟨n, hn⟩ : ∃ n, u n < r / 2 := ((tendsto_order.1 u_lim).2 _ (half_pos rpos)).exists, | |
obtain ⟨z, zc, hz⟩ : ∃ z ∈ c, dist x z < u n := | |
metric.mem_closure_iff.1 (h'c xs) _ (u_pos n), | |
refine ⟨(⟨z, zc⟩, n), _⟩, | |
change dist x (f (⟨z, zc⟩, n)) < r, | |
have A : (metric.ball z (u n) ∩ s).nonempty := ⟨x, hz, xs⟩, | |
dsimp [f], | |
simp only [A, dif_pos], | |
calc dist x A.some | |
≤ dist x z + dist z A.some : dist_triangle _ _ _ | |
... < r/2 + r/2 : add_lt_add (hz.trans hn) ((metric.mem_ball'.1 A.some_spec.1).trans hn) | |
... = r : add_halves _ | |
end | |
/-- The preimage of a separable set by an inducing map is separable. -/ | |
protected lemma _root_.inducing.is_separable_preimage {f : β → α} [topological_space β] | |
(hf : inducing f) {s : set α} (hs : is_separable s) : | |
is_separable (f ⁻¹' s) := | |
begin | |
haveI : second_countable_topology s, | |
{ haveI : separable_space s := hs.separable_space, | |
exact uniform_space.second_countable_of_separable _ }, | |
let g : f ⁻¹' s → s := cod_restrict (f ∘ coe) s (λ x, x.2), | |
have : inducing g := (hf.comp inducing_coe).cod_restrict _, | |
haveI : second_countable_topology (f ⁻¹' s) := this.second_countable_topology, | |
rw show f ⁻¹' s = coe '' (univ : set (f ⁻¹' s)), | |
by simpa only [image_univ, subtype.range_coe_subtype], | |
exact (is_separable_of_separable_space _).image continuous_subtype_coe | |
end | |
protected lemma _root_.embedding.is_separable_preimage {f : β → α} [topological_space β] | |
(hf : embedding f) {s : set α} (hs : is_separable s) : | |
is_separable (f ⁻¹' s) := | |
hf.to_inducing.is_separable_preimage hs | |
/-- If a map is continuous on a separable set `s`, then the image of `s` is also separable. -/ | |
lemma _root_.continuous_on.is_separable_image [topological_space β] {f : α → β} {s : set α} | |
(hf : continuous_on f s) (hs : is_separable s) : | |
is_separable (f '' s) := | |
begin | |
rw show f '' s = s.restrict f '' univ, by ext ; simp, | |
exact (is_separable_univ_iff.2 hs.separable_space).image | |
(continuous_on_iff_continuous_restrict.1 hf), | |
end | |
end metric | |
section pi | |
open finset | |
variables {π : β → Type*} [fintype β] [∀b, pseudo_metric_space (π b)] | |
/-- A finite product of pseudometric spaces is a pseudometric space, with the sup distance. -/ | |
noncomputable instance pseudo_metric_space_pi : pseudo_metric_space (Πb, π b) := | |
begin | |
/- we construct the instance from the pseudoemetric space instance to avoid checking again that | |
the uniformity is the same as the product uniformity, but we register nevertheless a nice formula | |
for the distance -/ | |
refine (pseudo_emetric_space.to_pseudo_metric_space_of_dist | |
(λf g : Π b, π b, ((sup univ (λb, nndist (f b) (g b)) : ℝ≥0) : ℝ)) | |
(λ f g, _) (λ f g, _)).replace_bornology (λ s, _), | |
show edist f g ≠ ⊤, | |
from ne_of_lt ((finset.sup_lt_iff bot_lt_top).2 $ λ b hb, edist_lt_top _ _), | |
show ↑(sup univ (λ b, nndist (f b) (g b))) = (sup univ (λ b, edist (f b) (g b))).to_real, | |
by simp only [edist_nndist, ← ennreal.coe_finset_sup, ennreal.coe_to_real], | |
show (pi.bornology s ↔ _ pseudo_metric_space.to_bornology _), | _|
{ simp only [← is_bounded_def, is_bounded_iff_eventually, ← forall_is_bounded_image_eval_iff, | |
ball_image_iff, ← eventually_all, function.eval_apply, (π _)], | |
refine eventually_congr ((eventually_ge_at_top 0).mono $ λ C hC, _), | |
lift C to ℝ≥0 using hC, | |
refine ⟨λ H x hx y hy, nnreal.coe_le_coe.2 $ finset.sup_le $ λ b hb, H b x hx y hy, | |
λ H b x hx y hy, nnreal.coe_le_coe.2 _⟩, | |
simpa only using finset.sup_le_iff.1 (nnreal.coe_le_coe.1 $ H hx hy) b (finset.mem_univ b) } | |
end | |
lemma nndist_pi_def (f g : Πb, π b) : nndist f g = sup univ (λb, nndist (f b) (g b)) := | |
nnreal.eq rfl | |
lemma dist_pi_def (f g : Πb, π b) : | |
dist f g = (sup univ (λb, nndist (f b) (g b)) : ℝ≥0) := rfl | |
@[simp] lemma dist_pi_const [nonempty β] (a b : α) : dist (λ x : β, a) (λ _, b) = dist a b := | |
by simpa only [dist_edist] using congr_arg ennreal.to_real (edist_pi_const a b) | |
@[simp] lemma nndist_pi_const [nonempty β] (a b : α) : | |
nndist (λ x : β, a) (λ _, b) = nndist a b := nnreal.eq $ dist_pi_const a b | |
lemma nndist_pi_le_iff {f g : Πb, π b} {r : ℝ≥0} : | |
nndist f g ≤ r ↔ ∀b, nndist (f b) (g b) ≤ r := | |
by simp [nndist_pi_def] | |
lemma dist_pi_lt_iff {f g : Πb, π b} {r : ℝ} (hr : 0 < r) : | |
dist f g < r ↔ ∀b, dist (f b) (g b) < r := | |
begin | |
lift r to ℝ≥0 using hr.le, | |
simp [dist_pi_def, finset.sup_lt_iff (show ⊥ < r, from hr)], | |
end | |
lemma dist_pi_le_iff {f g : Πb, π b} {r : ℝ} (hr : 0 ≤ r) : | |
dist f g ≤ r ↔ ∀b, dist (f b) (g b) ≤ r := | |
begin | |
lift r to ℝ≥0 using hr, | |
exact nndist_pi_le_iff | |
end | |
lemma nndist_le_pi_nndist (f g : Πb, π b) (b : β) : nndist (f b) (g b) ≤ nndist f g := | |
by { rw [nndist_pi_def], exact finset.le_sup (finset.mem_univ b) } | |
lemma dist_le_pi_dist (f g : Πb, π b) (b : β) : dist (f b) (g b) ≤ dist f g := | |
by simp only [dist_nndist, nnreal.coe_le_coe, nndist_le_pi_nndist f g b] | |
/-- An open ball in a product space is a product of open balls. See also `metric.ball_pi'` | |
for a version assuming `nonempty β` instead of `0 < r`. -/ | |
lemma ball_pi (x : Πb, π b) {r : ℝ} (hr : 0 < r) : | |
ball x r = set.pi univ (λ b, ball (x b) r) := | |
by { ext p, simp [dist_pi_lt_iff hr] } | |
/-- An open ball in a product space is a product of open balls. See also `metric.ball_pi` | |
for a version assuming `0 < r` instead of `nonempty β`. -/ | |
lemma ball_pi' [nonempty β] (x : Π b, π b) (r : ℝ) : | |
ball x r = set.pi univ (λ b, ball (x b) r) := | |
(lt_or_le 0 r).elim (ball_pi x) $ λ hr, by simp [ball_eq_empty.2 hr] | |
/-- A closed ball in a product space is a product of closed balls. See also `metric.closed_ball_pi'` | |
for a version assuming `nonempty β` instead of `0 ≤ r`. -/ | |
lemma closed_ball_pi (x : Πb, π b) {r : ℝ} (hr : 0 ≤ r) : | |
closed_ball x r = set.pi univ (λ b, closed_ball (x b) r) := | |
by { ext p, simp [dist_pi_le_iff hr] } | |
/-- A closed ball in a product space is a product of closed balls. See also `metric.closed_ball_pi` | |
for a version assuming `0 ≤ r` instead of `nonempty β`. -/ | |
lemma closed_ball_pi' [nonempty β] (x : Π b, π b) (r : ℝ) : | |
closed_ball x r = set.pi univ (λ b, closed_ball (x b) r) := | |
(le_or_lt 0 r).elim (closed_ball_pi x) $ λ hr, by simp [closed_ball_eq_empty.2 hr] | |
@[simp] lemma fin.nndist_insert_nth_insert_nth {n : ℕ} {α : fin (n + 1) → Type*} | |
[Π i, pseudo_metric_space (α i)] (i : fin (n + 1)) (x y : α i) (f g : Π j, α (i.succ_above j)) : | |
nndist (i.insert_nth x f) (i.insert_nth y g) = max (nndist x y) (nndist f g) := | |
eq_of_forall_ge_iff $ λ c, by simp [nndist_pi_le_iff, i.forall_iff_succ_above] | |
@[simp] lemma fin.dist_insert_nth_insert_nth {n : ℕ} {α : fin (n + 1) → Type*} | |
[Π i, pseudo_metric_space (α i)] (i : fin (n + 1)) (x y : α i) (f g : Π j, α (i.succ_above j)) : | |
dist (i.insert_nth x f) (i.insert_nth y g) = max (dist x y) (dist f g) := | |
by simp only [dist_nndist, fin.nndist_insert_nth_insert_nth, nnreal.coe_max] | |
lemma real.dist_le_of_mem_pi_Icc {x y x' y' : β → ℝ} (hx : x ∈ Icc x' y') (hy : y ∈ Icc x' y') : | |
dist x y ≤ dist x' y' := | |
begin | |
refine (dist_pi_le_iff dist_nonneg).2 (λ b, (real.dist_le_of_mem_interval _ _).trans | |
(dist_le_pi_dist _ _ b)); refine Icc_subset_interval _, | |
exacts [⟨hx.1 _, hx.2 _⟩, ⟨hy.1 _, hy.2 _⟩] | |
end | |
end pi | |
section compact | |
/-- Any compact set in a pseudometric space can be covered by finitely many balls of a given | |
positive radius -/ | |
lemma finite_cover_balls_of_compact {α : Type u} [pseudo_metric_space α] {s : set α} | |
(hs : is_compact s) {e : ℝ} (he : 0 < e) : | |
∃t ⊆ s, set.finite t ∧ s ⊆ ⋃x∈t, ball x e := | |
begin | |
apply hs.elim_finite_subcover_image, | |
{ simp [is_open_ball] }, | |
{ intros x xs, | |
simp, | |
exact ⟨x, ⟨xs, by simpa⟩⟩ } | |
end | |
alias finite_cover_balls_of_compact ← is_compact.finite_cover_balls | |
end compact | |
section proper_space | |
open metric | |
/-- A pseudometric space is proper if all closed balls are compact. -/ | |
class proper_space (α : Type u) [pseudo_metric_space α] : Prop := | |
(is_compact_closed_ball : ∀x:α, ∀r, is_compact (closed_ball x r)) | |
export proper_space (is_compact_closed_ball) | |
/-- In a proper pseudometric space, all spheres are compact. -/ | |
lemma is_compact_sphere {α : Type*} [pseudo_metric_space α] [proper_space α] (x : α) (r : ℝ) : | |
is_compact (sphere x r) := | |
compact_of_is_closed_subset (is_compact_closed_ball x r) is_closed_sphere sphere_subset_closed_ball | |
/-- In a proper pseudometric space, any sphere is a `compact_space` when considered as a subtype. -/ | |
instance {α : Type*} [pseudo_metric_space α] [proper_space α] (x : α) (r : ℝ) : | |
compact_space (sphere x r) := | |
is_compact_iff_compact_space.mp (is_compact_sphere _ _) | |
/-- A proper pseudo metric space is sigma compact, and therefore second countable. -/ | |
@[priority 100] -- see Note [lower instance priority] | |
instance second_countable_of_proper [proper_space α] : | |
second_countable_topology α := | |
begin | |
-- We already have `sigma_compact_space_of_locally_compact_second_countable`, so we don't | |
-- add an instance for `sigma_compact_space`. | |
suffices : sigma_compact_space α, by exactI emetric.second_countable_of_sigma_compact α, | |
rcases em (nonempty α) with ⟨⟨x⟩⟩|hn, | |
{ exact ⟨⟨λ n, closed_ball x n, λ n, is_compact_closed_ball _ _, Union_closed_ball_nat _⟩⟩ }, | |
{ exact ⟨⟨λ n, ∅, λ n, is_compact_empty, Union_eq_univ_iff.2 $ λ x, (hn ⟨x⟩).elim⟩⟩ } | |
end | |
lemma tendsto_dist_right_cocompact_at_top [proper_space α] (x : α) : | |
tendsto (λ y, dist y x) (cocompact α) at_top := | |
(has_basis_cocompact.tendsto_iff at_top_basis).2 $ λ r hr, | |
⟨closed_ball x r, is_compact_closed_ball x r, λ y hy, (not_le.1 $ mt mem_closed_ball.2 hy).le⟩ | |
lemma tendsto_dist_left_cocompact_at_top [proper_space α] (x : α) : | |
tendsto (dist x) (cocompact α) at_top := | |
by simpa only [dist_comm] using tendsto_dist_right_cocompact_at_top x | |
/-- If all closed balls of large enough radius are compact, then the space is proper. Especially | |
useful when the lower bound for the radius is 0. -/ | |
lemma proper_space_of_compact_closed_ball_of_le | |
(R : ℝ) (h : ∀x:α, ∀r, R ≤ r → is_compact (closed_ball x r)) : | |
proper_space α := | |
⟨begin | |
assume x r, | |
by_cases hr : R ≤ r, | |
{ exact h x r hr }, | |
{ have : closed_ball x r = closed_ball x R ∩ closed_ball x r, | |
{ symmetry, | |
apply inter_eq_self_of_subset_right, | |
exact closed_ball_subset_closed_ball (le_of_lt (not_le.1 hr)) }, | |
rw this, | |
exact (h x R le_rfl).inter_right is_closed_ball } | |
end⟩ | |
/- A compact pseudometric space is proper -/ | |
@[priority 100] -- see Note [lower instance priority] | |
instance proper_of_compact [compact_space α] : proper_space α := | |
⟨assume x r, is_closed_ball.is_compact⟩ | |
/-- A proper space is locally compact -/ | |
@[priority 100] -- see Note [lower instance priority] | |
instance locally_compact_of_proper [proper_space α] : | |
locally_compact_space α := | |
locally_compact_space_of_has_basis (λ x, nhds_basis_closed_ball) $ | |
λ x ε ε0, is_compact_closed_ball _ _ | |
/-- A proper space is complete -/ | |
@[priority 100] -- see Note [lower instance priority] | |
instance complete_of_proper [proper_space α] : complete_space α := | |
⟨begin | |
intros f hf, | |
/- We want to show that the Cauchy filter `f` is converging. It suffices to find a closed | |
ball (therefore compact by properness) where it is nontrivial. -/ | |
obtain ⟨t, t_fset, ht⟩ : ∃ t ∈ f, ∀ x y ∈ t, dist x y < 1 := | |
(metric.cauchy_iff.1 hf).2 1 zero_lt_one, | |
rcases hf.1.nonempty_of_mem t_fset with ⟨x, xt⟩, | |
have : closed_ball x 1 ∈ f := mem_of_superset t_fset (λ y yt, (ht y yt x xt).le), | |
rcases (compact_iff_totally_bounded_complete.1 (is_compact_closed_ball x 1)).2 f hf | |
(le_principal_iff.2 this) with ⟨y, -, hy⟩, | |
exact ⟨y, hy⟩ | |
end⟩ | |
/-- A finite product of proper spaces is proper. -/ | |
instance pi_proper_space {π : β → Type*} [fintype β] [∀b, pseudo_metric_space (π b)] | |
[h : ∀b, proper_space (π b)] : proper_space (Πb, π b) := | |
begin | |
refine proper_space_of_compact_closed_ball_of_le 0 (λx r hr, _), | |
rw closed_ball_pi _ hr, | |
apply is_compact_univ_pi (λb, _), | |
apply (h b).is_compact_closed_ball | |
end | |
variables [proper_space α] {x : α} {r : ℝ} {s : set α} | |
/-- If a nonempty ball in a proper space includes a closed set `s`, then there exists a nonempty | |
ball with the same center and a strictly smaller radius that includes `s`. -/ | |
lemma exists_pos_lt_subset_ball (hr : 0 < r) (hs : is_closed s) (h : s ⊆ ball x r) : | |
∃ r' ∈ Ioo 0 r, s ⊆ ball x r' := | |
begin | |
unfreezingI { rcases eq_empty_or_nonempty s with rfl|hne }, | |
{ exact ⟨r / 2, ⟨half_pos hr, half_lt_self hr⟩, empty_subset _⟩ }, | |
have : is_compact s, | |
from compact_of_is_closed_subset (is_compact_closed_ball x r) hs | |
(subset.trans h ball_subset_closed_ball), | |
obtain ⟨y, hys, hy⟩ : ∃ y ∈ s, s ⊆ closed_ball x (dist y x), | |
from this.exists_forall_ge hne (continuous_id.dist continuous_const).continuous_on, | |
have hyr : dist y x < r, from h hys, | |
rcases exists_between hyr with ⟨r', hyr', hrr'⟩, | |
exact ⟨r', ⟨dist_nonneg.trans_lt hyr', hrr'⟩, subset.trans hy $ closed_ball_subset_ball hyr'⟩ | |
end | |
/-- If a ball in a proper space includes a closed set `s`, then there exists a ball with the same | |
center and a strictly smaller radius that includes `s`. -/ | |
lemma exists_lt_subset_ball (hs : is_closed s) (h : s ⊆ ball x r) : | |
∃ r' < r, s ⊆ ball x r' := | |
begin | |
cases le_or_lt r 0 with hr hr, | |
{ rw [ball_eq_empty.2 hr, subset_empty_iff] at h, unfreezingI { subst s }, | |
exact (exists_lt r).imp (λ r' hr', ⟨hr', empty_subset _⟩) }, | |
{ exact (exists_pos_lt_subset_ball hr hs h).imp (λ r' hr', ⟨hr'.fst.2, hr'.snd⟩) } | |
end | |
end proper_space | |
lemma is_compact.is_separable {s : set α} (hs : is_compact s) : | |
is_separable s := | |
begin | |
haveI : compact_space s := is_compact_iff_compact_space.mp hs, | |
exact is_separable_of_separable_space_subtype s, | |
end | |
namespace metric | |
section second_countable | |
open topological_space | |
/-- A pseudometric space is second countable if, for every `ε > 0`, there is a countable set which | |
is `ε`-dense. -/ | |
lemma second_countable_of_almost_dense_set | |
(H : ∀ε > (0 : ℝ), ∃ s : set α, s.countable ∧ (∀x, ∃y ∈ s, dist x y ≤ ε)) : | |
second_countable_topology α := | |
begin | |
refine emetric.second_countable_of_almost_dense_set (λ ε ε0, _), | |
rcases ennreal.lt_iff_exists_nnreal_btwn.1 ε0 with ⟨ε', ε'0, ε'ε⟩, | |
choose s hsc y hys hyx using H ε' (by exact_mod_cast ε'0), | |
refine ⟨s, hsc, Union₂_eq_univ_iff.2 (λ x, ⟨y x, hys _, le_trans _ ε'ε.le⟩)⟩, | |
exact_mod_cast hyx x | |
end | |
end second_countable | |
end metric | |
lemma lebesgue_number_lemma_of_metric | |
{s : set α} {ι} {c : ι → set α} (hs : is_compact s) | |
(hc₁ : ∀ i, is_open (c i)) (hc₂ : s ⊆ ⋃ i, c i) : | |
∃ δ > 0, ∀ x ∈ s, ∃ i, ball x δ ⊆ c i := | |
let ⟨n, en, hn⟩ := lebesgue_number_lemma hs hc₁ hc₂, | |
⟨δ, δ0, hδ⟩ := mem_uniformity_dist.1 en in | |
⟨δ, δ0, assume x hx, let ⟨i, hi⟩ := hn x hx in | |
⟨i, assume y hy, hi (hδ (mem_ball'.mp hy))⟩⟩ | |
lemma lebesgue_number_lemma_of_metric_sUnion | |
{s : set α} {c : set (set α)} (hs : is_compact s) | |
(hc₁ : ∀ t ∈ c, is_open t) (hc₂ : s ⊆ ⋃₀ c) : | |
∃ δ > 0, ∀ x ∈ s, ∃ t ∈ c, ball x δ ⊆ t := | |
by rw sUnion_eq_Union at hc₂; | |
simpa using lebesgue_number_lemma_of_metric hs (by simpa) hc₂ | |
namespace metric | |
/-- Boundedness of a subset of a pseudometric space. We formulate the definition to work | |
even in the empty space. -/ | |
def bounded (s : set α) : Prop := | |
∃C, ∀x y ∈ s, dist x y ≤ C | |
section bounded | |
variables {x : α} {s t : set α} {r : ℝ} | |
lemma bounded_iff_is_bounded (s : set α) : bounded s ↔ is_bounded s := | |
begin | |
change bounded s ↔ sᶜ ∈ (cobounded α).sets, | |
simp [pseudo_metric_space.cobounded_sets, metric.bounded], | |
end | |
@[simp] lemma bounded_empty : bounded (∅ : set α) := | |
⟨0, by simp⟩ | |
lemma bounded_iff_mem_bounded : bounded s ↔ ∀ x ∈ s, bounded s := | |
⟨λ h _ _, h, λ H, | |
s.eq_empty_or_nonempty.elim | |
(λ hs, hs.symm ▸ bounded_empty) | |
(λ ⟨x, hx⟩, H x hx)⟩ | |
/-- Subsets of a bounded set are also bounded -/ | |
lemma bounded.mono (incl : s ⊆ t) : bounded t → bounded s := | |
Exists.imp $ λ C hC x hx y hy, hC x (incl hx) y (incl hy) | |
/-- Closed balls are bounded -/ | |
lemma bounded_closed_ball : bounded (closed_ball x r) := | |
⟨r + r, λ y hy z hz, begin | |
simp only [mem_closed_ball] at *, | |
calc dist y z ≤ dist y x + dist z x : dist_triangle_right _ _ _ | |
... ≤ r + r : add_le_add hy hz | |
end⟩ | |
/-- Open balls are bounded -/ | |
lemma bounded_ball : bounded (ball x r) := | |
bounded_closed_ball.mono ball_subset_closed_ball | |
/-- Spheres are bounded -/ | |
lemma bounded_sphere : bounded (sphere x r) := | |
bounded_closed_ball.mono sphere_subset_closed_ball | |
/-- Given a point, a bounded subset is included in some ball around this point -/ | |
lemma bounded_iff_subset_ball (c : α) : bounded s ↔ ∃r, s ⊆ closed_ball c r := | |
begin | |
split; rintro ⟨C, hC⟩, | |
{ cases s.eq_empty_or_nonempty with h h, | |
{ subst s, exact ⟨0, by simp⟩ }, | |
{ rcases h with ⟨x, hx⟩, | |
exact ⟨C + dist x c, λ y hy, calc | |
dist y c ≤ dist y x + dist x c : dist_triangle _ _ _ | |
... ≤ C + dist x c : add_le_add_right (hC y hy x hx) _⟩ } }, | |
{ exact bounded_closed_ball.mono hC } | |
end | |
lemma bounded.subset_ball (h : bounded s) (c : α) : ∃ r, s ⊆ closed_ball c r := | |
(bounded_iff_subset_ball c).1 h | |
lemma bounded.subset_ball_lt (h : bounded s) (a : ℝ) (c : α) : ∃ r, a < r ∧ s ⊆ closed_ball c r := | |
begin | |
rcases h.subset_ball c with ⟨r, hr⟩, | |
refine ⟨max r (a+1), lt_of_lt_of_le (by linarith) (le_max_right _ _), _⟩, | |
exact subset.trans hr (closed_ball_subset_closed_ball (le_max_left _ _)) | |
end | |
lemma bounded_closure_of_bounded (h : bounded s) : bounded (closure s) := | |
let ⟨C, h⟩ := h in | |
⟨C, λ a ha b hb, (is_closed_le' C).closure_subset $ map_mem_closure2 continuous_dist ha hb | |
$ ball_mem_comm.mp h⟩ | |
alias bounded_closure_of_bounded ← bounded.closure | |
@[simp] lemma bounded_closure_iff : bounded (closure s) ↔ bounded s := | |
⟨λ h, h.mono subset_closure, λ h, h.closure⟩ | |
/-- The union of two bounded sets is bounded. -/ | |
lemma bounded.union (hs : bounded s) (ht : bounded t) : bounded (s ∪ t) := | |
begin | |
refine bounded_iff_mem_bounded.2 (λ x _, _), | |
rw bounded_iff_subset_ball x at hs ht ⊢, | |
rcases hs with ⟨Cs, hCs⟩, rcases ht with ⟨Ct, hCt⟩, | |
exact ⟨max Cs Ct, union_subset | |
(subset.trans hCs $ closed_ball_subset_closed_ball $ le_max_left _ _) | |
(subset.trans hCt $ closed_ball_subset_closed_ball $ le_max_right _ _)⟩, | |
end | |
/-- The union of two sets is bounded iff each of the sets is bounded. -/ | |
@[simp] lemma bounded_union : bounded (s ∪ t) ↔ bounded s ∧ bounded t := | |
⟨λ h, ⟨h.mono (by simp), h.mono (by simp)⟩, λ h, h.1.union h.2⟩ | |
/-- A finite union of bounded sets is bounded -/ | |
lemma bounded_bUnion {I : set β} {s : β → set α} (H : I.finite) : | |
bounded (⋃i∈I, s i) ↔ ∀i ∈ I, bounded (s i) := | |
finite.induction_on H (by simp) $ λ x I _ _ IH, | |
by simp [or_imp_distrib, forall_and_distrib, IH] | |
protected lemma bounded.prod [pseudo_metric_space β] {s : set α} {t : set β} | |
(hs : bounded s) (ht : bounded t) : bounded (s ×ˢ t) := | |
begin | |
refine bounded_iff_mem_bounded.mpr (λ x hx, _), | |
rcases hs.subset_ball x.1 with ⟨rs, hrs⟩, | |
rcases ht.subset_ball x.2 with ⟨rt, hrt⟩, | |
suffices : s ×ˢ t ⊆ closed_ball x (max rs rt), | |
from bounded_closed_ball.mono this, | |
rw [← | .mk.eta _ _ x, ← closed_ball_prod_same],|
exact prod_mono (hrs.trans $ closed_ball_subset_closed_ball $ le_max_left _ _) | |
(hrt.trans $ closed_ball_subset_closed_ball $ le_max_right _ _) | |
end | |
/-- A totally bounded set is bounded -/ | |
lemma _root_.totally_bounded.bounded {s : set α} (h : totally_bounded s) : bounded s := | |
-- We cover the totally bounded set by finitely many balls of radius 1, | |
-- and then argue that a finite union of bounded sets is bounded | |
let ⟨t, fint, subs⟩ := (totally_bounded_iff.mp h) 1 zero_lt_one in | |
bounded.mono subs $ (bounded_bUnion fint).2 $ λ i hi, bounded_ball | |
/-- A compact set is bounded -/ | |
lemma _root_.is_compact.bounded {s : set α} (h : is_compact s) : bounded s := | |
-- A compact set is totally bounded, thus bounded | |
h.totally_bounded.bounded | |
/-- A finite set is bounded -/ | |
lemma bounded_of_finite {s : set α} (h : s.finite) : bounded s := | |
h.is_compact.bounded | |
alias bounded_of_finite ← _root_.set.finite.bounded | |
/-- A singleton is bounded -/ | |
lemma bounded_singleton {x : α} : bounded ({x} : set α) := | |
bounded_of_finite $ finite_singleton _ | |
/-- Characterization of the boundedness of the range of a function -/ | |
lemma bounded_range_iff {f : β → α} : bounded (range f) ↔ ∃C, ∀x y, dist (f x) (f y) ≤ C := | |
exists_congr $ λ C, ⟨ | |
λ H x y, H _ ⟨x, rfl⟩ _ ⟨y, rfl⟩, | |
by rintro H _ ⟨x, rfl⟩ _ ⟨y, rfl⟩; exact H x y⟩ | |
lemma bounded_range_of_tendsto_cofinite_uniformity {f : β → α} | |
(hf : tendsto (prod.map f f) (cofinite ×ᶠ cofinite) (𝓤 α)) : | |
bounded (range f) := | |
begin | |
rcases (has_basis_cofinite.prod_self.tendsto_iff uniformity_basis_dist).1 hf 1 zero_lt_one | |
with ⟨s, hsf, hs1⟩, | |
rw [← image_univ, ← union_compl_self s, image_union, bounded_union], | |
use [(hsf.image f).bounded, 1], | |
rintro _ ⟨x, hx, rfl⟩ _ ⟨y, hy, rfl⟩, | |
exact le_of_lt (hs1 (x, y) ⟨hx, hy⟩) | |
end | |
lemma bounded_range_of_cauchy_map_cofinite {f : β → α} (hf : cauchy (map f cofinite)) : | |
bounded (range f) := | |
bounded_range_of_tendsto_cofinite_uniformity $ (cauchy_map_iff.1 hf).2 | |
lemma _root_.cauchy_seq.bounded_range {f : ℕ → α} (hf : cauchy_seq f) : bounded (range f) := | |
bounded_range_of_cauchy_map_cofinite $ by rwa nat.cofinite_eq_at_top | |
lemma bounded_range_of_tendsto_cofinite {f : β → α} {a : α} (hf : tendsto f cofinite (𝓝 a)) : | |
bounded (range f) := | |
bounded_range_of_tendsto_cofinite_uniformity $ | |
(hf.prod_map hf).mono_right $ nhds_prod_eq.symm.trans_le (nhds_le_uniformity a) | |
/-- In a compact space, all sets are bounded -/ | |
lemma bounded_of_compact_space [compact_space α] : bounded s := | |
compact_univ.bounded.mono (subset_univ _) | |
lemma bounded_range_of_tendsto {α : Type*} [pseudo_metric_space α] (u : ℕ → α) {x : α} | |
(hu : tendsto u at_top (𝓝 x)) : | |
bounded (range u) := | |
hu.cauchy_seq.bounded_range | |
/-- The **Heine–Borel theorem**: In a proper space, a closed bounded set is compact. -/ | |
lemma is_compact_of_is_closed_bounded [proper_space α] (hc : is_closed s) (hb : bounded s) : | |
is_compact s := | |
begin | |
unfreezingI { rcases eq_empty_or_nonempty s with (rfl|⟨x, hx⟩) }, | |
{ exact is_compact_empty }, | |
{ rcases hb.subset_ball x with ⟨r, hr⟩, | |
exact compact_of_is_closed_subset (is_compact_closed_ball x r) hc hr } | |
end | |
/-- The **Heine–Borel theorem**: In a proper space, the closure of a bounded set is compact. -/ | |
lemma bounded.is_compact_closure [proper_space α] (h : bounded s) : | |
is_compact (closure s) := | |
is_compact_of_is_closed_bounded is_closed_closure h.closure | |
/-- The **Heine–Borel theorem**: | |
In a proper Hausdorff space, a set is compact if and only if it is closed and bounded. -/ | |
lemma compact_iff_closed_bounded [t2_space α] [proper_space α] : | |
is_compact s ↔ is_closed s ∧ bounded s := | |
⟨λ h, ⟨h.is_closed, h.bounded⟩, λ h, is_compact_of_is_closed_bounded h.1 h.2⟩ | |
lemma compact_space_iff_bounded_univ [proper_space α] : compact_space α ↔ bounded (univ : set α) := | |
⟨ | α _ _, λ hb, ⟨is_compact_of_is_closed_bounded is_closed_univ hb⟩⟩|
section conditionally_complete_linear_order | |
variables [preorder α] [compact_Icc_space α] | |
lemma bounded_Icc (a b : α) : bounded (Icc a b) := | |
(totally_bounded_Icc a b).bounded | |
lemma bounded_Ico (a b : α) : bounded (Ico a b) := | |
(totally_bounded_Ico a b).bounded | |
lemma bounded_Ioc (a b : α) : bounded (Ioc a b) := | |
(totally_bounded_Ioc a b).bounded | |
lemma bounded_Ioo (a b : α) : bounded (Ioo a b) := | |
(totally_bounded_Ioo a b).bounded | |
/-- In a pseudo metric space with a conditionally complete linear order such that the order and the | |
metric structure give the same topology, any order-bounded set is metric-bounded. -/ | |
lemma bounded_of_bdd_above_of_bdd_below {s : set α} (h₁ : bdd_above s) (h₂ : bdd_below s) : | |
bounded s := | |
let ⟨u, hu⟩ := h₁, ⟨l, hl⟩ := h₂ in | |
bounded.mono (λ x hx, mem_Icc.mpr ⟨hl hx, hu hx⟩) (bounded_Icc l u) | |
end conditionally_complete_linear_order | |
end bounded | |
section diam | |
variables {s : set α} {x y z : α} | |
/-- The diameter of a set in a metric space. To get controllable behavior even when the diameter | |
should be infinite, we express it in terms of the emetric.diameter -/ | |
noncomputable def diam (s : set α) : ℝ := ennreal.to_real (emetric.diam s) | |
/-- The diameter of a set is always nonnegative -/ | |
lemma diam_nonneg : 0 ≤ diam s := ennreal.to_real_nonneg | |
lemma diam_subsingleton (hs : s.subsingleton) : diam s = 0 := | |
by simp only [diam, emetric.diam_subsingleton hs, ennreal.zero_to_real] | |
/-- The empty set has zero diameter -/ | |
@[simp] lemma diam_empty : diam (∅ : set α) = 0 := | |
diam_subsingleton subsingleton_empty | |
/-- A singleton has zero diameter -/ | |
@[simp] lemma diam_singleton : diam ({x} : set α) = 0 := | |
diam_subsingleton subsingleton_singleton | |
-- Does not work as a simp-lemma, since {x, y} reduces to (insert y {x}) | |
lemma diam_pair : diam ({x, y} : set α) = dist x y := | |
by simp only [diam, emetric.diam_pair, dist_edist] | |
-- Does not work as a simp-lemma, since {x, y, z} reduces to (insert z (insert y {x})) | |
lemma diam_triple : | |
metric.diam ({x, y, z} : set α) = max (max (dist x y) (dist x z)) (dist y z) := | |
begin | |
simp only [metric.diam, emetric.diam_triple, dist_edist], | |
rw [ennreal.to_real_max, ennreal.to_real_max]; | |
apply_rules [ne_of_lt, edist_lt_top, max_lt] | |
end | |
/-- If the distance between any two points in a set is bounded by some constant `C`, | |
then `ennreal.of_real C` bounds the emetric diameter of this set. -/ | |
lemma ediam_le_of_forall_dist_le {C : ℝ} (h : ∀ (x ∈ s) (y ∈ s), dist x y ≤ C) : | |
emetric.diam s ≤ ennreal.of_real C := | |
emetric.diam_le $ | |
λ x hx y hy, (edist_dist x y).symm ▸ ennreal.of_real_le_of_real (h x hx y hy) | |
/-- If the distance between any two points in a set is bounded by some non-negative constant, | |
this constant bounds the diameter. -/ | |
lemma diam_le_of_forall_dist_le {C : ℝ} (h₀ : 0 ≤ C) (h : ∀ (x ∈ s) (y ∈ s), dist x y ≤ C) : | |
diam s ≤ C := | |
ennreal.to_real_le_of_le_of_real h₀ (ediam_le_of_forall_dist_le h) | |
/-- If the distance between any two points in a nonempty set is bounded by some constant, | |
this constant bounds the diameter. -/ | |
lemma diam_le_of_forall_dist_le_of_nonempty (hs : s.nonempty) {C : ℝ} | |
(h : ∀ (x ∈ s) (y ∈ s), dist x y ≤ C) : diam s ≤ C := | |
have h₀ : 0 ≤ C, from let ⟨x, hx⟩ := hs in le_trans dist_nonneg (h x hx x hx), | |
diam_le_of_forall_dist_le h₀ h | |
/-- The distance between two points in a set is controlled by the diameter of the set. -/ | |
lemma dist_le_diam_of_mem' (h : emetric.diam s ≠ ⊤) (hx : x ∈ s) (hy : y ∈ s) : | |
dist x y ≤ diam s := | |
begin | |
rw [diam, dist_edist], | |
rw ennreal.to_real_le_to_real (edist_ne_top _ _) h, | |
exact emetric.edist_le_diam_of_mem hx hy | |
end | |
/-- Characterize the boundedness of a set in terms of the finiteness of its emetric.diameter. -/ | |
lemma bounded_iff_ediam_ne_top : bounded s ↔ emetric.diam s ≠ ⊤ := | |
iff.intro | |
(λ ⟨C, hC⟩, ne_top_of_le_ne_top ennreal.of_real_ne_top $ ediam_le_of_forall_dist_le hC) | |
(λ h, ⟨diam s, λ x hx y hy, dist_le_diam_of_mem' h hx hy⟩) | |
lemma bounded.ediam_ne_top (h : bounded s) : emetric.diam s ≠ ⊤ := | |
bounded_iff_ediam_ne_top.1 h | |
lemma ediam_univ_eq_top_iff_noncompact [proper_space α] : | |
emetric.diam (univ : set α) = ∞ ↔ noncompact_space α := | |
by rw [← not_compact_space_iff, compact_space_iff_bounded_univ, bounded_iff_ediam_ne_top, not_not] | |
@[simp] lemma ediam_univ_of_noncompact [proper_space α] [noncompact_space α] : | |
emetric.diam (univ : set α) = ∞ := | |
ediam_univ_eq_top_iff_noncompact.mpr ‹_› | |
@[simp] lemma diam_univ_of_noncompact [proper_space α] [noncompact_space α] : | |
diam (univ : set α) = 0 := | |
by simp [diam] | |
/-- The distance between two points in a set is controlled by the diameter of the set. -/ | |
lemma dist_le_diam_of_mem (h : bounded s) (hx : x ∈ s) (hy : y ∈ s) : dist x y ≤ diam s := | |
dist_le_diam_of_mem' h.ediam_ne_top hx hy | |
lemma ediam_of_unbounded (h : ¬(bounded s)) : emetric.diam s = ∞ := | |
by rwa [bounded_iff_ediam_ne_top, not_not] at h | |
/-- An unbounded set has zero diameter. If you would prefer to get the value ∞, use `emetric.diam`. | |
This lemma makes it possible to avoid side conditions in some situations -/ | |
lemma diam_eq_zero_of_unbounded (h : ¬(bounded s)) : diam s = 0 := | |
by rw [diam, ediam_of_unbounded h, ennreal.top_to_real] | |
/-- If `s ⊆ t`, then the diameter of `s` is bounded by that of `t`, provided `t` is bounded. -/ | |
lemma diam_mono {s t : set α} (h : s ⊆ t) (ht : bounded t) : diam s ≤ diam t := | |
begin | |
unfold diam, | |
rw ennreal.to_real_le_to_real (bounded.mono h ht).ediam_ne_top ht.ediam_ne_top, | |
exact emetric.diam_mono h | |
end | |
/-- The diameter of a union is controlled by the sum of the diameters, and the distance between | |
any two points in each of the sets. This lemma is true without any side condition, since it is | |
obviously true if `s ∪ t` is unbounded. -/ | |
lemma diam_union {t : set α} (xs : x ∈ s) (yt : y ∈ t) : | |
diam (s ∪ t) ≤ diam s + dist x y + diam t := | |
begin | |
by_cases H : bounded (s ∪ t), | |
{ have hs : bounded s, from H.mono (subset_union_left _ _), | |
have ht : bounded t, from H.mono (subset_union_right _ _), | |
rw [bounded_iff_ediam_ne_top] at H hs ht, | |
rw [dist_edist, diam, diam, diam, ← ennreal.to_real_add, ← ennreal.to_real_add, | |
ennreal.to_real_le_to_real]; | |
repeat { apply ennreal.add_ne_top.2; split }; try { assumption }; | |
try { apply edist_ne_top }, | |
exact emetric.diam_union xs yt }, | |
{ rw [diam_eq_zero_of_unbounded H], | |
apply_rules [add_nonneg, diam_nonneg, dist_nonneg] } | |
end | |
/-- If two sets intersect, the diameter of the union is bounded by the sum of the diameters. -/ | |
lemma diam_union' {t : set α} (h : (s ∩ t).nonempty) : diam (s ∪ t) ≤ diam s + diam t := | |
begin | |
rcases h with ⟨x, ⟨xs, xt⟩⟩, | |
simpa using diam_union xs xt | |
end | |
lemma diam_le_of_subset_closed_ball {r : ℝ} (hr : 0 ≤ r) (h : s ⊆ closed_ball x r) : | |
diam s ≤ 2 * r := | |
diam_le_of_forall_dist_le (mul_nonneg zero_le_two hr) $ λa ha b hb, calc | |
dist a b ≤ dist a x + dist b x : dist_triangle_right _ _ _ | |
... ≤ r + r : add_le_add (h ha) (h hb) | |
... = 2 * r : by simp [mul_two, mul_comm] | |
/-- The diameter of a closed ball of radius `r` is at most `2 r`. -/ | |
lemma diam_closed_ball {r : ℝ} (h : 0 ≤ r) : diam (closed_ball x r) ≤ 2 * r := | |
diam_le_of_subset_closed_ball h subset.rfl | |
/-- The diameter of a ball of radius `r` is at most `2 r`. -/ | |
lemma diam_ball {r : ℝ} (h : 0 ≤ r) : diam (ball x r) ≤ 2 * r := | |
diam_le_of_subset_closed_ball h ball_subset_closed_ball | |
/-- If a family of complete sets with diameter tending to `0` is such that each finite intersection | |
is nonempty, then the total intersection is also nonempty. -/ | |
lemma _root_.is_complete.nonempty_Inter_of_nonempty_bInter {s : ℕ → set α} (h0 : is_complete (s 0)) | |
(hs : ∀ n, is_closed (s n)) (h's : ∀ n, bounded (s n)) (h : ∀ N, (⋂ n ≤ N, s n).nonempty) | |
(h' : tendsto (λ n, diam (s n)) at_top (𝓝 0)) : | |
(⋂ n, s n).nonempty := | |
begin | |
let u := λ N, (h N).some, | |
have I : ∀ n N, n ≤ N → u N ∈ s n, | |
{ assume n N hn, | |
apply mem_of_subset_of_mem _ ((h N).some_spec), | |
assume x hx, | |
simp only [mem_Inter] at hx, | |
exact hx n hn }, | |
have : ∀ n, u n ∈ s 0 := λ n, I 0 n (zero_le _), | |
have : cauchy_seq u, | |
{ apply cauchy_seq_of_le_tendsto_0 _ _ h', | |
assume m n N hm hn, | |
exact dist_le_diam_of_mem (h's N) (I _ _ hm) (I _ _ hn) }, | |
obtain ⟨x, hx, xlim⟩ : ∃ (x : α) (H : x ∈ s 0), tendsto (λ (n : ℕ), u n) at_top (𝓝 x) := | |
cauchy_seq_tendsto_of_is_complete h0 (λ n, I 0 n (zero_le _)) this, | |
refine ⟨x, mem_Inter.2 (λ n, _)⟩, | |
apply (hs n).mem_of_tendsto xlim, | |
filter_upwards [Ici_mem_at_top n] with p hp, | |
exact I n p hp, | |
end | |
/-- In a complete space, if a family of closed sets with diameter tending to `0` is such that each | |
finite intersection is nonempty, then the total intersection is also nonempty. -/ | |
lemma nonempty_Inter_of_nonempty_bInter [complete_space α] {s : ℕ → set α} | |
(hs : ∀ n, is_closed (s n)) (h's : ∀ n, bounded (s n)) (h : ∀ N, (⋂ n ≤ N, s n).nonempty) | |
(h' : tendsto (λ n, diam (s n)) at_top (𝓝 0)) : | |
(⋂ n, s n).nonempty := | |
(hs 0).is_complete.nonempty_Inter_of_nonempty_bInter hs h's h h' | |
end diam | |
end metric | |
lemma comap_dist_right_at_top_le_cocompact (x : α) : comap (λ y, dist y x) at_top ≤ cocompact α := | |
begin | |
refine filter.has_basis_cocompact.ge_iff.2 (λ s hs, mem_comap.2 _), | |
rcases hs.bounded.subset_ball x with ⟨r, hr⟩, | |
exact ⟨Ioi r, Ioi_mem_at_top r, λ y hy hys, (mem_closed_ball.1 $ hr hys).not_lt hy⟩ | |
end | |
lemma comap_dist_left_at_top_le_cocompact (x : α) : comap (dist x) at_top ≤ cocompact α := | |
by simpa only [dist_comm _ x] using comap_dist_right_at_top_le_cocompact x | |
lemma comap_dist_right_at_top_eq_cocompact [proper_space α] (x : α) : | |
comap (λ y, dist y x) at_top = cocompact α := | |
(comap_dist_right_at_top_le_cocompact x).antisymm $ (tendsto_dist_right_cocompact_at_top x).le_comap | |
lemma comap_dist_left_at_top_eq_cocompact [proper_space α] (x : α) : | |
comap (dist x) at_top = cocompact α := | |
(comap_dist_left_at_top_le_cocompact x).antisymm $ (tendsto_dist_left_cocompact_at_top x).le_comap | |
lemma tendsto_cocompact_of_tendsto_dist_comp_at_top {f : β → α} {l : filter β} (x : α) | |
(h : tendsto (λ y, dist (f y) x) l at_top) : tendsto f l (cocompact α) := | |
by { refine tendsto.mono_right _ (comap_dist_right_at_top_le_cocompact x), rwa tendsto_comap_iff } | |
namespace int | |
open metric | |
/-- Under the coercion from `ℤ` to `ℝ`, inverse images of compact sets are finite. -/ | |
lemma tendsto_coe_cofinite : tendsto (coe : ℤ → ℝ) cofinite (cocompact ℝ) := | |
begin | |
refine tendsto_cocompact_of_tendsto_dist_comp_at_top (0 : ℝ) _, | |
simp only [filter.tendsto_at_top, eventually_cofinite, not_le, ← mem_ball], | |
change ∀ r : ℝ, (coe ⁻¹' (ball (0 : ℝ) r)).finite, | |
simp [real.ball_eq_Ioo, set.finite_Ioo], | |
end | |
end int | |
/-- We now define `metric_space`, extending `pseudo_metric_space`. -/ | |
class metric_space (α : Type u) extends pseudo_metric_space α : Type u := | |
(eq_of_dist_eq_zero : ∀ {x y : α}, dist x y = 0 → x = y) | |
/-- Two metric space structures with the same distance coincide. -/ | |
@[ext] lemma metric_space.ext {α : Type*} {m m' : metric_space α} | |
(h : m.to_has_dist = m'.to_has_dist) : m = m' := | |
begin | |
have h' : m.to_pseudo_metric_space = m'.to_pseudo_metric_space := pseudo_metric_space.ext h, | |
unfreezingI { rcases m, rcases m' }, | |
dsimp at h', | |
unfreezingI { subst h' }, | |
end | |
/-- Construct a metric space structure whose underlying topological space structure | |
(definitionally) agrees which a pre-existing topology which is compatible with a given distance | |
function. -/ | |
def metric_space.of_metrizable {α : Type*} [topological_space α] (dist : α → α → ℝ) | |
(dist_self : ∀ x : α, dist x x = 0) | |
(dist_comm : ∀ x y : α, dist x y = dist y x) | |
(dist_triangle : ∀ x y z : α, dist x z ≤ dist x y + dist y z) | |
(H : ∀ s : set α, is_open s ↔ ∀ x ∈ s, ∃ ε > 0, ∀ y, dist x y < ε → y ∈ s) | |
(eq_of_dist_eq_zero : ∀ x y : α, dist x y = 0 → x = y) : metric_space α := | |
{ eq_of_dist_eq_zero := eq_of_dist_eq_zero, | |
..pseudo_metric_space.of_metrizable dist dist_self dist_comm dist_triangle H } | |
variables {γ : Type w} [metric_space γ] | |
theorem eq_of_dist_eq_zero {x y : γ} : dist x y = 0 → x = y := | |
metric_space.eq_of_dist_eq_zero | |
@[simp] theorem dist_eq_zero {x y : γ} : dist x y = 0 ↔ x = y := | |
iff.intro eq_of_dist_eq_zero (assume : x = y, this ▸ dist_self _) | |
@[simp] theorem zero_eq_dist {x y : γ} : 0 = dist x y ↔ x = y := | |
by rw [eq_comm, dist_eq_zero] | |
theorem dist_ne_zero {x y : γ} : dist x y ≠ 0 ↔ x ≠ y := | |
by simpa only [not_iff_not] using dist_eq_zero | |
@[simp] theorem dist_le_zero {x y : γ} : dist x y ≤ 0 ↔ x = y := | |
by simpa [le_antisymm_iff, dist_nonneg] using _ _ x y | |
@[simp] theorem dist_pos {x y : γ} : 0 < dist x y ↔ x ≠ y := | |
by simpa only [not_le] using not_congr dist_le_zero | |
theorem eq_of_forall_dist_le {x y : γ} (h : ∀ ε > 0, dist x y ≤ ε) : x = y := | |
eq_of_dist_eq_zero (eq_of_le_of_forall_le_of_dense dist_nonneg h) | |
/--Deduce the equality of points with the vanishing of the nonnegative distance-/ | |
theorem eq_of_nndist_eq_zero {x y : γ} : nndist x y = 0 → x = y := | |
by simp only [← nnreal.eq_iff, ← dist_nndist, imp_self, nnreal.coe_zero, dist_eq_zero] | |
/--Characterize the equality of points with the vanishing of the nonnegative distance-/ | |
@[simp] theorem nndist_eq_zero {x y : γ} : nndist x y = 0 ↔ x = y := | |
by simp only [← nnreal.eq_iff, ← dist_nndist, imp_self, nnreal.coe_zero, dist_eq_zero] | |
@[simp] theorem zero_eq_nndist {x y : γ} : 0 = nndist x y ↔ x = y := | |
by simp only [← nnreal.eq_iff, ← dist_nndist, imp_self, nnreal.coe_zero, zero_eq_dist] | |
namespace metric | |
variables {x : γ} {s : set γ} | |
@[simp] lemma closed_ball_zero : closed_ball x 0 = {x} := | |
set.ext $ λ y, dist_le_zero | |
@[simp] lemma sphere_zero : sphere x 0 = {x} := | |
set.ext $ λ y, dist_eq_zero | |
lemma subsingleton_closed_ball (x : γ) {r : ℝ} (hr : r ≤ 0) : (closed_ball x r).subsingleton := | |
begin | |
rcases hr.lt_or_eq with hr|rfl, | |
{ rw closed_ball_eq_empty.2 hr, exact subsingleton_empty }, | |
{ rw closed_ball_zero, exact subsingleton_singleton } | |
end | |
lemma subsingleton_sphere (x : γ) {r : ℝ} (hr : r ≤ 0) : (sphere x r).subsingleton := | |
(subsingleton_closed_ball x hr).mono sphere_subset_closed_ball | |
/-- A map between metric spaces is a uniform embedding if and only if the distance between `f x` | |
and `f y` is controlled in terms of the distance between `x` and `y` and conversely. -/ | |
theorem uniform_embedding_iff' [metric_space β] {f : γ → β} : | |
uniform_embedding f ↔ | |
(∀ ε > 0, ∃ δ > 0, ∀ {a b : γ}, dist a b < δ → dist (f a) (f b) < ε) ∧ | |
(∀ δ > 0, ∃ ε > 0, ∀ {a b : γ}, dist (f a) (f b) < ε → dist a b < δ) := | |
begin | |
split, | |
{ assume h, | |
exact ⟨uniform_continuous_iff.1 (uniform_embedding_iff.1 h).2.1, | |
(uniform_embedding_iff.1 h).2.2⟩ }, | |
{ rintros ⟨h₁, h₂⟩, | |
refine uniform_embedding_iff.2 ⟨_, uniform_continuous_iff.2 h₁, h₂⟩, | |
assume x y hxy, | |
have : dist x y ≤ 0, | |
{ refine le_of_forall_lt' (λδ δpos, _), | |
rcases h₂ δ δpos with ⟨ε, εpos, hε⟩, | |
have : dist (f x) (f y) < ε, by simpa [hxy], | |
exact hε this }, | |
simpa using this } | |
end | |
@[priority 100] -- see Note [lower instance priority] | |
instance _root_.metric_space.to_separated : separated_space γ := | |
separated_def.2 $ λ x y h, eq_of_forall_dist_le $ | |
λ ε ε0, le_of_lt (h _ (dist_mem_uniformity ε0)) | |
/-- If a `pseudo_metric_space` is a T₀ space, then it is a `metric_space`. -/ | |
def of_t0_pseudo_metric_space (α : Type*) [pseudo_metric_space α] [t0_space α] : | |
metric_space α := | |
{ eq_of_dist_eq_zero := λ x y hdist, inseparable.eq $ metric.inseparable_iff.2 hdist, | |
..‹pseudo_metric_space α› } | |
/-- A metric space induces an emetric space -/ | |
@[priority 100] -- see Note [lower instance priority] | |
instance metric_space.to_emetric_space : emetric_space γ := | |
emetric.of_t0_pseudo_emetric_space γ | |
lemma is_closed_of_pairwise_le_dist {s : set γ} {ε : ℝ} (hε : 0 < ε) | |
(hs : s.pairwise (λ x y, ε ≤ dist x y)) : is_closed s := | |
is_closed_of_spaced_out (dist_mem_uniformity hε) $ by simpa using hs | |
lemma closed_embedding_of_pairwise_le_dist {α : Type*} [topological_space α] [discrete_topology α] | |
{ε : ℝ} (hε : 0 < ε) {f : α → γ} (hf : pairwise (λ x y, ε ≤ dist (f x) (f y))) : | |
closed_embedding f := | |
closed_embedding_of_spaced_out (dist_mem_uniformity hε) $ by simpa using hf | |
/-- If `f : β → α` sends any two distinct points to points at distance at least `ε > 0`, then | |
`f` is a uniform embedding with respect to the discrete uniformity on `β`. -/ | |
lemma uniform_embedding_bot_of_pairwise_le_dist {β : Type*} {ε : ℝ} (hε : 0 < ε) {f : β → α} | |
(hf : pairwise (λ x y, ε ≤ dist (f x) (f y))) : | _ _ ⊥ (by apply_instance) f :=|
uniform_embedding_of_spaced_out (dist_mem_uniformity hε) $ by simpa using hf | |
end metric | |
/-- Build a new metric space from an old one where the bundled uniform structure is provably | |
(but typically non-definitionaly) equal to some given uniform structure. | |
See Note [forgetful inheritance]. | |
-/ | |
def metric_space.replace_uniformity {γ} [U : uniform_space γ] (m : metric_space γ) | |
(H : | _ U = _ pseudo_emetric_space.to_uniform_space) :|
metric_space γ := | |
{ eq_of_dist_eq_zero := | _ _,|
..pseudo_metric_space.replace_uniformity m.to_pseudo_metric_space H, } | |
lemma metric_space.replace_uniformity_eq {γ} [U : uniform_space γ] (m : metric_space γ) | |
(H : | _ U = _ pseudo_emetric_space.to_uniform_space) :|
m.replace_uniformity H = m := | |
by { ext, refl } | |
/-- Build a new metric space from an old one where the bundled topological structure is provably | |
(but typically non-definitionaly) equal to some given topological structure. | |
See Note [forgetful inheritance]. | |
-/ | |
@[reducible] def metric_space.replace_topology {γ} [U : topological_space γ] (m : metric_space γ) | |
(H : U = m.to_pseudo_metric_space.to_uniform_space.to_topological_space) : | |
metric_space γ := | |
.replace_uniformity γ (m.to_uniform_space.replace_topology H) m rfl | |
lemma metric_space.replace_topology_eq {γ} [U : topological_space γ] (m : metric_space γ) | |
(H : U = m.to_pseudo_metric_space.to_uniform_space.to_topological_space) : | |
m.replace_topology H = m := | |
by { ext, refl } | |
/-- One gets a metric space from an emetric space if the edistance | |
is everywhere finite, by pushing the edistance to reals. We set it up so that the edist and the | |
uniformity are defeq in the metric space and the emetric space. In this definition, the distance | |
is given separately, to be able to prescribe some expression which is not defeq to the push-forward | |
of the edistance to reals. -/ | |
def emetric_space.to_metric_space_of_dist {α : Type u} [e : emetric_space α] | |
(dist : α → α → ℝ) | |
(edist_ne_top : ∀x y: α, edist x y ≠ ⊤) | |
(h : ∀x y, dist x y = ennreal.to_real (edist x y)) : | |
metric_space α := | |
{ dist := dist, | |
eq_of_dist_eq_zero := λx y hxy, | |
by simpa [h, ennreal.to_real_eq_zero_iff, edist_ne_top x y] using hxy, | |
..pseudo_emetric_space.to_pseudo_metric_space_of_dist dist edist_ne_top h, } | |
/-- One gets a metric space from an emetric space if the edistance | |
is everywhere finite, by pushing the edistance to reals. We set it up so that the edist and the | |
uniformity are defeq in the metric space and the emetric space. -/ | |
def emetric_space.to_metric_space {α : Type u} [e : emetric_space α] (h : ∀x y: α, edist x y ≠ ⊤) : | |
metric_space α := | |
emetric_space.to_metric_space_of_dist (λx y, ennreal.to_real (edist x y)) h (λx y, rfl) | |
/-- Build a new metric space from an old one where the bundled bornology structure is provably | |
(but typically non-definitionaly) equal to some given bornology structure. | |
See Note [forgetful inheritance]. | |
-/ | |
def metric_space.replace_bornology {α} [B : bornology α] (m : metric_space α) | |
(H : ∀ s, | _ B s ↔ _ pseudo_metric_space.to_bornology s) :|
metric_space α := | |
{ to_bornology := B, | |
.. pseudo_metric_space.replace_bornology _ H, | |
.. m } | |
lemma metric_space.replace_bornology_eq {α} [m : metric_space α] [B : bornology α] | |
(H : ∀ s, | _ B s ↔ _ pseudo_metric_space.to_bornology s) :|
metric_space.replace_bornology _ H = m := | |
by { ext, refl } | |
/-- Metric space structure pulled back by an injective function. Injectivity is necessary to | |
ensure that `dist x y = 0` only if `x = y`. -/ | |
def metric_space.induced {γ β} (f : γ → β) (hf : function.injective f) | |
(m : metric_space β) : metric_space γ := | |
{ eq_of_dist_eq_zero := λ x y h, hf (dist_eq_zero.1 h), | |
..pseudo_metric_space.induced f m.to_pseudo_metric_space } | |
/-- Pull back a metric space structure by a uniform embedding. This is a version of | |
`metric_space.induced` useful in case if the domain already has a `uniform_space` structure. -/ | |
@[reducible] def uniform_embedding.comap_metric_space | |
{α β} [uniform_space α] [metric_space β] (f : α → β) (h : uniform_embedding f) : | |
metric_space α := | |
(metric_space.induced f h.inj ‹_›).replace_uniformity h.comap_uniformity.symm | |
/-- Pull back a metric space structure by an embedding. This is a version of | |
`metric_space.induced` useful in case if the domain already has a `topological_space` structure. -/ | |
@[reducible] def embedding.comap_metric_space | |
{α β} [topological_space α] [metric_space β] (f : α → β) (h : embedding f) : | |
metric_space α := | |
begin | |
letI : uniform_space α := embedding.comap_uniform_space f h, | |
exact uniform_embedding.comap_metric_space f (h.to_uniform_embedding f), | |
end | |
instance subtype.metric_space {α : Type*} {p : α → Prop} [metric_space α] : | |
metric_space (subtype p) := | |
metric_space.induced coe subtype.coe_injective ‹_› | |
@[to_additive] instance {α : Type*} [metric_space α] : metric_space (αᵐᵒᵖ) := | |
metric_space.induced mul_opposite.unop mul_opposite.unop_injective ‹_› | |
local attribute [instance] filter.unique | |
instance : metric_space empty := | |
{ dist := λ _ _, 0, | |
dist_self := λ _, rfl, | |
dist_comm := λ _ _, rfl, | |
eq_of_dist_eq_zero := λ _ _ _, subsingleton.elim _ _, | |
dist_triangle := λ _ _ _, show (0:ℝ) ≤ 0 + 0, by rw add_zero, | |
to_uniform_space := empty.uniform_space, | |
uniformity_dist := subsingleton.elim _ _ } | |
instance : metric_space punit.{u + 1} := | |
{ dist := λ _ _, 0, | |
dist_self := λ _, rfl, | |
dist_comm := λ _ _, rfl, | |
eq_of_dist_eq_zero := λ _ _ _, subsingleton.elim _ _, | |
dist_triangle := λ _ _ _, show (0:ℝ) ≤ 0 + 0, by rw add_zero, | |
to_uniform_space := punit.uniform_space, | |
uniformity_dist := | |
begin | |
simp only, | |
haveI : ne_bot (⨅ ε > (0 : ℝ), 𝓟 {p : punit.{u + 1} × punit.{u + 1} | 0 < ε}), | |
{ exact 0) (λ _, rfl) (λ _ _, rfl) | .ne_bot _ (uniform_space_of_dist (λ _ _,|
(λ _ _ _, by rw zero_add)) _ }, | |
refine (eq_top_of_ne_bot _).trans (eq_top_of_ne_bot _).symm, | |
end} | |
section real | |
/-- Instantiate the reals as a metric space. -/ | |
noncomputable instance real.metric_space : metric_space ℝ := | |
{ eq_of_dist_eq_zero := λ x y h, by simpa [dist, sub_eq_zero] using h, | |
..real.pseudo_metric_space } | |
end real | |
section nnreal | |
noncomputable instance : metric_space ℝ≥0 := subtype.metric_space | |
end nnreal | |
instance [metric_space β] : metric_space (ulift β) := | |
metric_space.induced ulift.down ulift.down_injective ‹_› | |
section prod | |
noncomputable instance prod.metric_space_max [metric_space β] : metric_space (γ × β) := | |
{ eq_of_dist_eq_zero := λ x y h, begin | |
cases max_le_iff.1 (le_of_eq h) with h₁ h₂, | |
exact prod.ext_iff.2 ⟨dist_le_zero.1 h₁, dist_le_zero.1 h₂⟩ | |
end, | |
..prod.pseudo_metric_space_max, } | |
end prod | |
section pi | |
open finset | |
variables {π : β → Type*} [fintype β] [∀b, metric_space (π b)] | |
/-- A finite product of metric spaces is a metric space, with the sup distance. -/ | |
noncomputable instance metric_space_pi : metric_space (Πb, π b) := | |
/- we construct the instance from the emetric space instance to avoid checking again that the | |
uniformity is the same as the product uniformity, but we register nevertheless a nice formula | |
for the distance -/ | |
{ eq_of_dist_eq_zero := assume f g eq0, | |
begin | |
have eq1 : edist f g = 0 := by simp only [edist_dist, eq0, ennreal.of_real_zero], | |
have eq2 : sup univ (λ (b : β), edist (f b) (g b)) ≤ 0 := le_of_eq eq1, | |
simp only [finset.sup_le_iff] at eq2, | |
exact (funext $ assume b, edist_le_zero.1 $ eq2 b $ mem_univ b) | |
end, | |
..pseudo_metric_space_pi } | |
end pi | |
namespace metric | |
section second_countable | |
open topological_space | |
/-- A metric space is second countable if one can reconstruct up to any `ε>0` any element of the | |
space from countably many data. -/ | |
lemma second_countable_of_countable_discretization {α : Type u} [metric_space α] | |
(H : ∀ε > (0 : ℝ), ∃ (β : Type*) (_ : encodable β) (F : α → β), ∀x y, F x = F y → dist x y ≤ ε) : | |
second_countable_topology α := | |
begin | |
cases (univ : set α).eq_empty_or_nonempty with hs hs, | |
{ haveI : compact_space α := ⟨by rw hs; exact is_compact_empty⟩, by apply_instance }, | |
rcases hs with ⟨x0, hx0⟩, | |
letI : inhabited α := ⟨x0⟩, | |
refine second_countable_of_almost_dense_set (λε ε0, _), | |
rcases H ε ε0 with ⟨β, fβ, F, hF⟩, | |
resetI, | |
let Finv := function.inv_fun F, | |
refine ⟨range Finv, ⟨countable_range _, λx, _⟩⟩, | |
let x' := Finv (F x), | |
have : F x' = F x := function.inv_fun_eq ⟨x, rfl⟩, | |
exact ⟨x', mem_range_self _, hF _ _ this.symm⟩ | |
end | |
end second_countable | |
end metric | |
section eq_rel | |
/-- The canonical equivalence relation on a pseudometric space. -/ | |
def pseudo_metric.dist_setoid (α : Type u) [pseudo_metric_space α] : setoid α := | |
setoid.mk (λx y, dist x y = 0) | |
begin | |
unfold equivalence, | |
repeat { split }, | |
{ exact pseudo_metric_space.dist_self }, | |
{ assume x y h, rwa pseudo_metric_space.dist_comm }, | |
{ assume x y z hxy hyz, | |
refine le_antisymm _ dist_nonneg, | |
calc dist x z ≤ dist x y + dist y z : pseudo_metric_space.dist_triangle _ _ _ | |
... = 0 + 0 : by rw [hxy, hyz] | |
... = 0 : by simp } | |
end | |
local attribute [instance] pseudo_metric.dist_setoid | |
/-- The canonical quotient of a pseudometric space, identifying points at distance `0`. -/ | |
@[reducible] definition pseudo_metric_quot (α : Type u) [pseudo_metric_space α] : Type* := | |
quotient (pseudo_metric.dist_setoid α) | |
instance has_dist_metric_quot {α : Type u} [pseudo_metric_space α] : | |
has_dist (pseudo_metric_quot α) := | |
{ dist := quotient.lift₂ (λp q : α, dist p q) | |
begin | |
assume x y x' y' hxx' hyy', | |
have Hxx' : dist x x' = 0 := hxx', | |
have Hyy' : dist y y' = 0 := hyy', | |
have A : dist x y ≤ dist x' y' := calc | |
dist x y ≤ dist x x' + dist x' y : pseudo_metric_space.dist_triangle _ _ _ | |
... = dist x' y : by simp [Hxx'] | |
... ≤ dist x' y' + dist y' y : pseudo_metric_space.dist_triangle _ _ _ | |
... = dist x' y' : by simp [pseudo_metric_space.dist_comm, Hyy'], | |
have B : dist x' y' ≤ dist x y := calc | |
dist x' y' ≤ dist x' x + dist x y' : pseudo_metric_space.dist_triangle _ _ _ | |
... = dist x y' : by simp [pseudo_metric_space.dist_comm, Hxx'] | |
... ≤ dist x y + dist y y' : pseudo_metric_space.dist_triangle _ _ _ | |
... = dist x y : by simp [Hyy'], | |
exact le_antisymm A B | |
end } | |
lemma pseudo_metric_quot_dist_eq {α : Type u} [pseudo_metric_space α] (p q : α) : | |
dist ⟦p⟧ ⟦q⟧ = dist p q := rfl | |
instance metric_space_quot {α : Type u} [pseudo_metric_space α] : | |
metric_space (pseudo_metric_quot α) := | |
{ dist_self := begin | |
refine quotient.ind (λy, _), | |
exact pseudo_metric_space.dist_self _ | |
end, | |
eq_of_dist_eq_zero := λxc yc, by exact quotient.induction_on₂ xc yc (λx y H, quotient.sound H), | |
dist_comm := | |
λxc yc, quotient.induction_on₂ xc yc (λx y, pseudo_metric_space.dist_comm _ _), | |
dist_triangle := | |
λxc yc zc, quotient.induction_on₃ xc yc zc (λx y z, pseudo_metric_space.dist_triangle _ _ _) } | |
end eq_rel | |
/-! | |
### `additive`, `multiplicative` | |
The distance on those type synonyms is inherited without change. | |
-/ | |
open additive multiplicative | |
section | |
variables [has_dist X] | |
instance : has_dist (additive X) := ‹has_dist X› | |
instance : has_dist (multiplicative X) := ‹has_dist X› | |
@[simp] lemma dist_of_mul (a b : X) : dist (of_mul a) (of_mul b) = dist a b := rfl | |
@[simp] lemma dist_of_add (a b : X) : dist (of_add a) (of_add b) = dist a b := rfl | |
@[simp] lemma dist_to_mul (a b : additive X) : dist (to_mul a) (to_mul b) = dist a b := rfl | |
@[simp] lemma dist_to_add (a b : multiplicative X) : dist (to_add a) (to_add b) = dist a b := rfl | |
end | |
section | |
variables [pseudo_metric_space X] | |
instance : pseudo_metric_space (additive X) := ‹pseudo_metric_space X› | |
instance : pseudo_metric_space (multiplicative X) := ‹pseudo_metric_space X› | |
@[simp] lemma nndist_of_mul (a b : X) : nndist (of_mul a) (of_mul b) = nndist a b := rfl | |
@[simp] lemma nndist_of_add (a b : X) : nndist (of_add a) (of_add b) = nndist a b := rfl | |
@[simp] lemma nndist_to_mul (a b : additive X) : nndist (to_mul a) (to_mul b) = nndist a b := rfl | |
@[simp] lemma nndist_to_add (a b : multiplicative X) : nndist (to_add a) (to_add b) = nndist a b := | |
rfl | |
end | |
instance [metric_space X] : metric_space (additive X) := ‹metric_space X› | |
instance [metric_space X] : metric_space (multiplicative X) := ‹metric_space X› | |
instance [pseudo_metric_space X] [proper_space X] : proper_space (additive X) := ‹proper_space X› | |
instance [pseudo_metric_space X] [proper_space X] : proper_space (multiplicative X) := | |
‹proper_space X› | |
/-! | |
### Order dual | |
The distance on this type synonym is inherited without change. | |
-/ | |
open order_dual | |
section | |
variables [has_dist X] | |
instance : has_dist Xᵒᵈ := ‹has_dist X› | |
@[simp] lemma dist_to_dual (a b : X) : dist (to_dual a) (to_dual b) = dist a b := rfl | |
@[simp] lemma dist_of_dual (a b : Xᵒᵈ) : dist (of_dual a) (of_dual b) = dist a b := rfl | |
end | |
section | |
variables [pseudo_metric_space X] | |
instance : pseudo_metric_space Xᵒᵈ := ‹pseudo_metric_space X› | |
@[simp] lemma nndist_to_dual (a b : X) : nndist (to_dual a) (to_dual b) = nndist a b := rfl | |
@[simp] lemma nndist_of_dual (a b : Xᵒᵈ) : nndist (of_dual a) (of_dual b) = nndist a b := rfl | |
end | |
instance [metric_space X] : metric_space Xᵒᵈ := ‹metric_space X› | |
instance [pseudo_metric_space X] [proper_space X] : proper_space Xᵒᵈ := ‹proper_space X› | |