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/- | |
Copyright (c) 2019 Reid Barton. All rights reserved. | |
Released under Apache 2.0 license as described in the file LICENSE. | |
Authors: Johannes Hölzl | |
-/ | |
import topology.constructions | |
import topology.algebra.monoid | |
/-! | |
# Topology on lists and vectors | |
-/ | |
open topological_space set filter | |
open_locale topological_space filter | |
variables {α : Type*} {β : Type*} [topological_space α] [topological_space β] | |
instance : topological_space (list α) := | |
topological_space.mk_of_nhds (traverse nhds) | |
lemma nhds_list (as : list α) : 𝓝 as = traverse 𝓝 as := | |
begin | |
refine nhds_mk_of_nhds _ _ _ _, | |
{ assume l, induction l, | |
case list.nil { exact le_rfl }, | |
case list.cons : a l ih | |
{ suffices : list.cons <$> pure a <*> pure l ≤ list.cons <$> 𝓝 a <*> traverse 𝓝 l, | |
{ simpa only [] with functor_norm using this }, | |
exact filter.seq_mono (filter.map_mono $ pure_le_nhds a) ih } }, | |
{ assume l s hs, | |
rcases (mem_traverse_iff _ _).1 hs with ⟨u, hu, hus⟩, clear as hs, | |
have : ∃v:list (set α), l.forall₂ (λa s, is_open s ∧ a ∈ s) v ∧ sequence v ⊆ s, | |
{ induction hu generalizing s, | |
case list.forall₂.nil : hs this | |
{ existsi [], simpa only [list.forall₂_nil_left_iff, exists_eq_left] }, | |
case list.forall₂.cons : a s as ss ht h ih t hts | |
{ rcases mem_nhds_iff.1 ht with ⟨u, hut, hu⟩, | |
rcases ih (subset.refl _) with ⟨v, hv, hvss⟩, | |
exact ⟨u::v, list.forall₂.cons hu hv, | |
subset.trans (set.seq_mono (set.image_subset _ hut) hvss) hts⟩ } }, | |
rcases this with ⟨v, hv, hvs⟩, | |
refine ⟨sequence v, mem_traverse _ _ _, hvs, _⟩, | |
{ exact hv.imp (assume a s ⟨hs, ha⟩, is_open.mem_nhds hs ha) }, | |
{ assume u hu, | |
have hu := (list.mem_traverse _ _).1 hu, | |
have : list.forall₂ (λa s, is_open s ∧ a ∈ s) u v, | |
{ refine list.forall₂.flip _, | |
replace hv := hv.flip, | |
simp only [list.forall₂_and_left, flip] at ⊢ hv, | |
exact ⟨hv.1, hu.flip⟩ }, | |
refine mem_of_superset _ hvs, | |
exact mem_traverse _ _ (this.imp $ assume a s ⟨hs, ha⟩, is_open.mem_nhds hs ha) } } | |
end | |
@[simp] lemma nhds_nil : 𝓝 ([] : list α) = pure [] := | |
by rw [nhds_list, list.traverse_nil _]; apply_instance | |
lemma nhds_cons (a : α) (l : list α) : | |
𝓝 (a :: l) = list.cons <$> 𝓝 a <*> 𝓝 l := | |
by rw [nhds_list, list.traverse_cons _, ← nhds_list]; apply_instance | |
lemma list.tendsto_cons {a : α} {l : list α} : | |
tendsto (λp:α×list α, list.cons p.1 p.2) (𝓝 a ×ᶠ 𝓝 l) (𝓝 (a :: l)) := | |
by rw [nhds_cons, tendsto, filter.map_prod]; exact le_rfl | |
lemma filter.tendsto.cons {α : Type*} {f : α → β} {g : α → list β} | |
{a : _root_.filter α} {b : β} {l : list β} (hf : tendsto f a (𝓝 b)) (hg : tendsto g a (𝓝 l)) : | |
tendsto (λa, list.cons (f a) (g a)) a (𝓝 (b :: l)) := | |
list.tendsto_cons.comp (tendsto.prod_mk hf hg) | |
namespace list | |
lemma tendsto_cons_iff {β : Type*} {f : list α → β} {b : _root_.filter β} {a : α} {l : list α} : | |
tendsto f (𝓝 (a :: l)) b ↔ tendsto (λp:α×list α, f (p.1 :: p.2)) (𝓝 a ×ᶠ 𝓝 l) b := | |
have 𝓝 (a :: l) = (𝓝 a ×ᶠ 𝓝 l).map (λp:α×list α, (p.1 :: p.2)), | |
begin | |
simp only | |
[nhds_cons, filter.prod_eq, (filter.map_def _ _).symm, (filter.seq_eq_filter_seq _ _).symm], | |
simp [-filter.seq_eq_filter_seq, -filter.map_def, (∘)] with functor_norm, | |
end, | |
by rw [this, filter.tendsto_map'_iff] | |
lemma continuous_cons : continuous (λ x : α × list α, (x.1 :: x.2 : list α)) := | |
continuous_iff_continuous_at.mpr $ λ ⟨x, y⟩, continuous_at_fst.cons continuous_at_snd | |
lemma tendsto_nhds {β : Type*} {f : list α → β} {r : list α → _root_.filter β} | |
(h_nil : tendsto f (pure []) (r [])) | |
(h_cons : ∀l a, tendsto f (𝓝 l) (r l) → | |
tendsto (λp:α×list α, f (p.1 :: p.2)) (𝓝 a ×ᶠ 𝓝 l) (r (a::l))) : | |
∀l, tendsto f (𝓝 l) (r l) | |
| [] := by rwa [nhds_nil] | |
| (a::l) := by rw [tendsto_cons_iff]; exact h_cons l a (tendsto_nhds l) | |
lemma continuous_at_length : | |
∀(l : list α), continuous_at list.length l := | |
begin | |
simp only [continuous_at, nhds_discrete], | |
refine tendsto_nhds _ _, | |
{ exact tendsto_pure_pure _ _ }, | |
{ assume l a ih, | |
dsimp only [list.length], | |
refine tendsto.comp (tendsto_pure_pure (λx, x + 1) _) _, | |
refine tendsto.comp ih tendsto_snd } | |
end | |
lemma tendsto_insert_nth' {a : α} : ∀{n : ℕ} {l : list α}, | |
tendsto (λp:α×list α, insert_nth n p.1 p.2) (𝓝 a ×ᶠ 𝓝 l) (𝓝 (insert_nth n a l)) | |
| 0 l := tendsto_cons | |
| (n+1) [] := by simp | |
| (n+1) (a'::l) := | |
have 𝓝 a ×ᶠ 𝓝 (a' :: l) = | |
(𝓝 a ×ᶠ (𝓝 a' ×ᶠ 𝓝 l)).map (λp:α×α×list α, (p.1, p.2.1 :: p.2.2)), | |
begin | |
simp only [nhds_cons, filter.prod_eq, ← filter.map_def, ← filter.seq_eq_filter_seq], | |
simp [-filter.seq_eq_filter_seq, -filter.map_def, (∘)] with functor_norm | |
end, | |
begin | |
rw [this, tendsto_map'_iff], | |
exact (tendsto_fst.comp tendsto_snd).cons | |
((@tendsto_insert_nth' n l).comp $ tendsto_fst.prod_mk $ tendsto_snd.comp tendsto_snd) | |
end | |
lemma tendsto_insert_nth {β} {n : ℕ} {a : α} {l : list α} {f : β → α} {g : β → list α} | |
{b : _root_.filter β} (hf : tendsto f b (𝓝 a)) (hg : tendsto g b (𝓝 l)) : | |
tendsto (λb:β, insert_nth n (f b) (g b)) b (𝓝 (insert_nth n a l)) := | |
tendsto_insert_nth'.comp (tendsto.prod_mk hf hg) | |
lemma continuous_insert_nth {n : ℕ} : continuous (λp:α×list α, insert_nth n p.1 p.2) := | |
continuous_iff_continuous_at.mpr $ | |
assume ⟨a, l⟩, by rw [continuous_at, nhds_prod_eq]; exact tendsto_insert_nth' | |
lemma tendsto_remove_nth : ∀{n : ℕ} {l : list α}, | |
tendsto (λl, remove_nth l n) (𝓝 l) (𝓝 (remove_nth l n)) | |
| _ [] := by rw [nhds_nil]; exact tendsto_pure_nhds _ _ | |
| 0 (a::l) := by rw [tendsto_cons_iff]; exact tendsto_snd | |
| (n+1) (a::l) := | |
begin | |
rw [tendsto_cons_iff], | |
dsimp [remove_nth], | |
exact tendsto_fst.cons ((@tendsto_remove_nth n l).comp tendsto_snd) | |
end | |
lemma continuous_remove_nth {n : ℕ} : continuous (λl : list α, remove_nth l n) := | |
continuous_iff_continuous_at.mpr $ assume a, tendsto_remove_nth | |
@[to_additive] | |
lemma tendsto_prod [monoid α] [has_continuous_mul α] {l : list α} : | |
tendsto list.prod (𝓝 l) (𝓝 l.prod) := | |
begin | |
induction l with x l ih, | |
{ simp [nhds_nil, mem_of_mem_nhds, tendsto_pure_left] {contextual := tt} }, | |
simp_rw [tendsto_cons_iff, prod_cons], | |
have := continuous_iff_continuous_at.mp continuous_mul (x, l.prod), | |
rw [continuous_at, nhds_prod_eq] at this, | |
exact this.comp (tendsto_id.prod_map ih) | |
end | |
@[to_additive] | |
lemma continuous_prod [monoid α] [has_continuous_mul α] : continuous (prod : list α → α) := | |
continuous_iff_continuous_at.mpr $ λ l, tendsto_prod | |
end list | |
namespace vector | |
open list | |
instance (n : ℕ) : topological_space (vector α n) := | |
by unfold vector; apply_instance | |
lemma tendsto_cons {n : ℕ} {a : α} {l : vector α n}: | |
tendsto (λp:α×vector α n, p.1 ::ᵥ p.2) (𝓝 a ×ᶠ 𝓝 l) (𝓝 (a ::ᵥ l)) := | |
by { simp [tendsto_subtype_rng, ←subtype.val_eq_coe, cons_val], | |
exact tendsto_fst.cons (tendsto.comp continuous_at_subtype_coe tendsto_snd) } | |
lemma tendsto_insert_nth | |
{n : ℕ} {i : fin (n+1)} {a:α} : | |
∀{l:vector α n}, tendsto (λp:α×vector α n, insert_nth p.1 i p.2) | |
(𝓝 a ×ᶠ 𝓝 l) (𝓝 (insert_nth a i l)) | |
| ⟨l, hl⟩ := | |
begin | |
rw [insert_nth, tendsto_subtype_rng], | |
simp [insert_nth_val], | |
exact list.tendsto_insert_nth tendsto_fst (tendsto.comp continuous_at_subtype_coe tendsto_snd : _) | |
end | |
lemma continuous_insert_nth' {n : ℕ} {i : fin (n+1)} : | |
continuous (λp:α×vector α n, insert_nth p.1 i p.2) := | |
continuous_iff_continuous_at.mpr $ assume ⟨a, l⟩, | |
by rw [continuous_at, nhds_prod_eq]; exact tendsto_insert_nth | |
lemma continuous_insert_nth {n : ℕ} {i : fin (n+1)} | |
{f : β → α} {g : β → vector α n} (hf : continuous f) (hg : continuous g) : | |
continuous (λb, insert_nth (f b) i (g b)) := | |
continuous_insert_nth'.comp (hf.prod_mk hg : _) | |
lemma continuous_at_remove_nth {n : ℕ} {i : fin (n+1)} : | |
∀{l:vector α (n+1)}, continuous_at (remove_nth i) l | |
| ⟨l, hl⟩ := | |
-- ∀{l:vector α (n+1)}, tendsto (remove_nth i) (𝓝 l) (𝓝 (remove_nth i l)) | |
--| ⟨l, hl⟩ := | |
begin | |
rw [continuous_at, remove_nth, tendsto_subtype_rng], | |
simp only [← subtype.val_eq_coe, vector.remove_nth_val], | |
exact tendsto.comp list.tendsto_remove_nth continuous_at_subtype_coe, | |
end | |
lemma continuous_remove_nth {n : ℕ} {i : fin (n+1)} : | |
continuous (remove_nth i : vector α (n+1) → vector α n) := | |
continuous_iff_continuous_at.mpr $ assume ⟨a, l⟩, continuous_at_remove_nth | |
end vector | |