Datasets:
Tasks:
Text Generation
Modalities:
Text
Sub-tasks:
language-modeling
Languages:
English
Size:
100K - 1M
License:
File size: 24,832 Bytes
4365a98 fc5e983 4365a98 fc5e983 4365a98 fc5e983 4365a98 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Mario Carneiro, Patrick Massot
-/
import topology.order
/-!
# Specific classes of maps between topological spaces
This file introduces the following properties of a map `f : X → Y` between topological spaces:
* `is_open_map f` means the image of an open set under `f` is open.
* `is_closed_map f` means the image of a closed set under `f` is closed.
(Open and closed maps need not be continuous.)
* `inducing f` means the topology on `X` is the one induced via `f` from the topology on `Y`.
These behave like embeddings except they need not be injective. Instead, points of `X` which
are identified by `f` are also inseparable in the topology on `X`.
* `embedding f` means `f` is inducing and also injective. Equivalently, `f` identifies `X` with
a subspace of `Y`.
* `open_embedding f` means `f` is an embedding with open image, so it identifies `X` with an
open subspace of `Y`. Equivalently, `f` is an embedding and an open map.
* `closed_embedding f` similarly means `f` is an embedding with closed image, so it identifies
`X` with a closed subspace of `Y`. Equivalently, `f` is an embedding and a closed map.
* `quotient_map f` is the dual condition to `embedding f`: `f` is surjective and the topology
on `Y` is the one coinduced via `f` from the topology on `X`. Equivalently, `f` identifies
`Y` with a quotient of `X`. Quotient maps are also sometimes known as identification maps.
## References
* <https://en.wikipedia.org/wiki/Open_and_closed_maps>
* <https://en.wikipedia.org/wiki/Embedding#General_topology>
* <https://en.wikipedia.org/wiki/Quotient_space_(topology)#Quotient_map>
## Tags
open map, closed map, embedding, quotient map, identification map
-/
open set filter function
open_locale topological_space filter
variables {α : Type*} {β : Type*} {γ : Type*} {δ : Type*}
section inducing
/-- A function `f : α → β` between topological spaces is inducing if the topology on `α` is induced
by the topology on `β` through `f`, meaning that a set `s : set α` is open iff it is the preimage
under `f` of some open set `t : set β`. -/
@[mk_iff]
structure inducing [tα : topological_space α] [tβ : topological_space β] (f : α → β) : Prop :=
(induced : tα = tβ.induced f)
variables [topological_space α] [topological_space β] [topological_space γ] [topological_space δ]
lemma inducing_id : inducing (@id α) :=
⟨induced_id.symm⟩
protected lemma inducing.comp {g : β → γ} {f : α → β} (hg : inducing g) (hf : inducing f) :
inducing (g ∘ f) :=
⟨by rw [hf.induced, hg.induced, induced_compose]⟩
lemma inducing_of_inducing_compose {f : α → β} {g : β → γ} (hf : continuous f) (hg : continuous g)
(hgf : inducing (g ∘ f)) : inducing f :=
⟨le_antisymm
(by rwa ← continuous_iff_le_induced)
(by { rw [hgf.induced, ← continuous_iff_le_induced], apply hg.comp continuous_induced_dom })⟩
lemma inducing_iff_nhds {f : α → β} : inducing f ↔ ∀ a, 𝓝 a = comap f (𝓝 (f a)) :=
(inducing_iff _).trans (induced_iff_nhds_eq f)
lemma inducing.nhds_eq_comap {f : α → β} (hf : inducing f) :
∀ (a : α), 𝓝 a = comap f (𝓝 $ f a) :=
inducing_iff_nhds.1 hf
lemma inducing.map_nhds_eq {f : α → β} (hf : inducing f) (a : α) :
(𝓝 a).map f = 𝓝[range f] (f a) :=
hf.induced.symm ▸ map_nhds_induced_eq a
lemma inducing.map_nhds_of_mem {f : α → β} (hf : inducing f) (a : α) (h : range f ∈ 𝓝 (f a)) :
(𝓝 a).map f = 𝓝 (f a) :=
hf.induced.symm ▸ map_nhds_induced_of_mem h
lemma inducing.image_mem_nhds_within {f : α → β} (hf : inducing f) {a : α} {s : set α}
(hs : s ∈ 𝓝 a) : f '' s ∈ 𝓝[range f] (f a) :=
hf.map_nhds_eq a ▸ image_mem_map hs
lemma inducing.tendsto_nhds_iff {ι : Type*}
{f : ι → β} {g : β → γ} {a : filter ι} {b : β} (hg : inducing g) :
tendsto f a (𝓝 b) ↔ tendsto (g ∘ f) a (𝓝 (g b)) :=
by rw [hg.nhds_eq_comap, tendsto_comap_iff]
lemma inducing.continuous_at_iff {f : α → β} {g : β → γ} (hg : inducing g) {x : α} :
continuous_at f x ↔ continuous_at (g ∘ f) x :=
by simp_rw [continuous_at, inducing.tendsto_nhds_iff hg]
lemma inducing.continuous_iff {f : α → β} {g : β → γ} (hg : inducing g) :
continuous f ↔ continuous (g ∘ f) :=
by simp_rw [continuous_iff_continuous_at, hg.continuous_at_iff]
lemma inducing.continuous_at_iff' {f : α → β} {g : β → γ} (hf : inducing f) {x : α}
(h : range f ∈ 𝓝 (f x)) : continuous_at (g ∘ f) x ↔ continuous_at g (f x) :=
by { simp_rw [continuous_at, filter.tendsto, ← hf.map_nhds_of_mem _ h, filter.map_map] }
protected lemma inducing.continuous {f : α → β} (hf : inducing f) : continuous f :=
hf.continuous_iff.mp continuous_id
protected lemma inducing.inducing_iff {f : α → β} {g : β → γ} (hg : inducing g) :
inducing f ↔ inducing (g ∘ f) :=
begin
refine ⟨λ h, hg.comp h, λ hgf, inducing_of_inducing_compose _ hg.continuous hgf⟩,
rw hg.continuous_iff,
exact hgf.continuous
end
lemma inducing.closure_eq_preimage_closure_image {f : α → β} (hf : inducing f) (s : set α) :
closure s = f ⁻¹' closure (f '' s) :=
by { ext x, rw [set.mem_preimage, ← closure_induced, hf.induced] }
lemma inducing.is_closed_iff {f : α → β} (hf : inducing f) {s : set α} :
is_closed s ↔ ∃ t, is_closed t ∧ f ⁻¹' t = s :=
by rw [hf.induced, is_closed_induced_iff]
lemma inducing.is_closed_iff' {f : α → β} (hf : inducing f) {s : set α} :
is_closed s ↔ ∀ x, f x ∈ closure (f '' s) → x ∈ s :=
by rw [hf.induced, is_closed_induced_iff']
lemma inducing.is_closed_preimage {f : α → β} (h : inducing f) (s : set β) (hs : is_closed s) :
is_closed (f ⁻¹' s) :=
(inducing.is_closed_iff h).mpr ⟨s, hs, rfl⟩
lemma inducing.is_open_iff {f : α → β} (hf : inducing f) {s : set α} :
is_open s ↔ ∃ t, is_open t ∧ f ⁻¹' t = s :=
by rw [hf.induced, is_open_induced_iff]
lemma inducing.dense_iff {f : α → β} (hf : inducing f) {s : set α} :
dense s ↔ ∀ x, f x ∈ closure (f '' s) :=
by simp only [dense, hf.closure_eq_preimage_closure_image, mem_preimage]
end inducing
section embedding
/-- A function between topological spaces is an embedding if it is injective,
and for all `s : set α`, `s` is open iff it is the preimage of an open set. -/
@[mk_iff] structure embedding [tα : topological_space α] [tβ : topological_space β] (f : α → β)
extends inducing f : Prop :=
(inj : injective f)
lemma function.injective.embedding_induced [t : topological_space β]
{f : α → β} (hf : injective f) :
@_root_.embedding α β (t.induced f) t f :=
{ induced := rfl,
inj := hf }
variables [topological_space α] [topological_space β] [topological_space γ]
lemma embedding.mk' (f : α → β) (inj : injective f)
(induced : ∀ a, comap f (𝓝 (f a)) = 𝓝 a) : embedding f :=
⟨inducing_iff_nhds.2 (λ a, (induced a).symm), inj⟩
lemma embedding_id : embedding (@id α) :=
⟨inducing_id, assume a₁ a₂ h, h⟩
lemma embedding.comp {g : β → γ} {f : α → β} (hg : embedding g) (hf : embedding f) :
embedding (g ∘ f) :=
{ inj:= assume a₁ a₂ h, hf.inj $ hg.inj h,
..hg.to_inducing.comp hf.to_inducing }
lemma embedding_of_embedding_compose {f : α → β} {g : β → γ} (hf : continuous f) (hg : continuous g)
(hgf : embedding (g ∘ f)) : embedding f :=
{ induced := (inducing_of_inducing_compose hf hg hgf.to_inducing).induced,
inj := assume a₁ a₂ h, hgf.inj $ by simp [h, (∘)] }
protected lemma function.left_inverse.embedding {f : α → β} {g : β → α}
(h : left_inverse f g) (hf : continuous f) (hg : continuous g) :
embedding g :=
embedding_of_embedding_compose hg hf $ h.comp_eq_id.symm ▸ embedding_id
lemma embedding.map_nhds_eq {f : α → β} (hf : embedding f) (a : α) :
(𝓝 a).map f = 𝓝[range f] (f a) :=
hf.1.map_nhds_eq a
lemma embedding.map_nhds_of_mem {f : α → β}
(hf : embedding f) (a : α) (h : range f ∈ 𝓝 (f a)) : (𝓝 a).map f = 𝓝 (f a) :=
hf.1.map_nhds_of_mem a h
lemma embedding.tendsto_nhds_iff {ι : Type*}
{f : ι → β} {g : β → γ} {a : filter ι} {b : β} (hg : embedding g) :
tendsto f a (𝓝 b) ↔ tendsto (g ∘ f) a (𝓝 (g b)) :=
hg.to_inducing.tendsto_nhds_iff
lemma embedding.continuous_iff {f : α → β} {g : β → γ} (hg : embedding g) :
continuous f ↔ continuous (g ∘ f) :=
inducing.continuous_iff hg.1
lemma embedding.continuous {f : α → β} (hf : embedding f) : continuous f :=
inducing.continuous hf.1
lemma embedding.closure_eq_preimage_closure_image {e : α → β} (he : embedding e) (s : set α) :
closure s = e ⁻¹' closure (e '' s) :=
he.1.closure_eq_preimage_closure_image s
end embedding
/-- A function between topological spaces is a quotient map if it is surjective,
and for all `s : set β`, `s` is open iff its preimage is an open set. -/
def quotient_map {α : Type*} {β : Type*} [tα : topological_space α] [tβ : topological_space β]
(f : α → β) : Prop :=
surjective f ∧ tβ = tα.coinduced f
lemma quotient_map_iff {α β : Type*} [topological_space α] [topological_space β] {f : α → β} :
quotient_map f ↔ surjective f ∧ ∀ s : set β, is_open s ↔ is_open (f ⁻¹' s) :=
and_congr iff.rfl topological_space_eq_iff
namespace quotient_map
variables [topological_space α] [topological_space β] [topological_space γ] [topological_space δ]
{g : β → γ} {f : α → β}
protected lemma id : quotient_map (@id α) :=
⟨assume a, ⟨a, rfl⟩, coinduced_id.symm⟩
protected lemma comp (hg : quotient_map g) (hf : quotient_map f) :
quotient_map (g ∘ f) :=
⟨hg.left.comp hf.left, by rw [hg.right, hf.right, coinduced_compose]⟩
protected lemma of_quotient_map_compose (hf : continuous f) (hg : continuous g)
(hgf : quotient_map (g ∘ f)) : quotient_map g :=
⟨hgf.1.of_comp,
le_antisymm
(by { rw [hgf.right, ← continuous_iff_coinduced_le], apply continuous_coinduced_rng.comp hf })
(by rwa ← continuous_iff_coinduced_le)⟩
lemma of_inverse {g : β → α} (hf : continuous f) (hg : continuous g) (h : left_inverse g f) :
quotient_map g :=
quotient_map.of_quotient_map_compose hf hg $ h.comp_eq_id.symm ▸ quotient_map.id
protected lemma continuous_iff (hf : quotient_map f) :
continuous g ↔ continuous (g ∘ f) :=
by rw [continuous_iff_coinduced_le, continuous_iff_coinduced_le, hf.right, coinduced_compose]
protected lemma continuous (hf : quotient_map f) : continuous f :=
hf.continuous_iff.mp continuous_id
protected lemma surjective (hf : quotient_map f) : surjective f := hf.1
protected lemma is_open_preimage (hf : quotient_map f) {s : set β} :
is_open (f ⁻¹' s) ↔ is_open s :=
((quotient_map_iff.1 hf).2 s).symm
protected lemma is_closed_preimage (hf : quotient_map f) {s : set β} :
is_closed (f ⁻¹' s) ↔ is_closed s :=
by simp only [← is_open_compl_iff, ← preimage_compl, hf.is_open_preimage]
end quotient_map
/-- A map `f : α → β` is said to be an *open map*, if the image of any open `U : set α`
is open in `β`. -/
def is_open_map [topological_space α] [topological_space β] (f : α → β) :=
∀ U : set α, is_open U → is_open (f '' U)
namespace is_open_map
variables [topological_space α] [topological_space β] [topological_space γ] {f : α → β}
protected lemma id : is_open_map (@id α) := assume s hs, by rwa [image_id]
protected lemma comp
{g : β → γ} {f : α → β} (hg : is_open_map g) (hf : is_open_map f) : is_open_map (g ∘ f) :=
by intros s hs; rw [image_comp]; exact hg _ (hf _ hs)
lemma is_open_range (hf : is_open_map f) : is_open (range f) :=
by { rw ← image_univ, exact hf _ is_open_univ }
lemma image_mem_nhds (hf : is_open_map f) {x : α} {s : set α} (hx : s ∈ 𝓝 x) :
f '' s ∈ 𝓝 (f x) :=
let ⟨t, hts, ht, hxt⟩ := mem_nhds_iff.1 hx in
mem_of_superset (is_open.mem_nhds (hf t ht) (mem_image_of_mem _ hxt)) (image_subset _ hts)
lemma range_mem_nhds (hf : is_open_map f) (x : α) : range f ∈ 𝓝 (f x) :=
hf.is_open_range.mem_nhds $ mem_range_self _
lemma maps_to_interior (hf : is_open_map f) {s : set α} {t : set β} (h : maps_to f s t) :
maps_to f (interior s) (interior t) :=
maps_to'.2 $ interior_maximal (h.mono interior_subset subset.rfl).image_subset
(hf _ is_open_interior)
lemma image_interior_subset (hf : is_open_map f) (s : set α) :
f '' interior s ⊆ interior (f '' s) :=
(hf.maps_to_interior (maps_to_image f s)).image_subset
lemma nhds_le (hf : is_open_map f) (a : α) : 𝓝 (f a) ≤ (𝓝 a).map f :=
le_map $ λ s, hf.image_mem_nhds
lemma of_nhds_le (hf : ∀ a, 𝓝 (f a) ≤ map f (𝓝 a)) : is_open_map f :=
λ s hs, is_open_iff_mem_nhds.2 $ λ b ⟨a, has, hab⟩,
hab ▸ hf _ (image_mem_map $ is_open.mem_nhds hs has)
lemma of_sections {f : α → β}
(h : ∀ x, ∃ g : β → α, continuous_at g (f x) ∧ g (f x) = x ∧ right_inverse g f) :
is_open_map f :=
of_nhds_le $ λ x, let ⟨g, hgc, hgx, hgf⟩ := h x in
calc 𝓝 (f x) = map f (map g (𝓝 (f x))) : by rw [map_map, hgf.comp_eq_id, map_id]
... ≤ map f (𝓝 (g (f x))) : map_mono hgc
... = map f (𝓝 x) : by rw hgx
lemma of_inverse {f : α → β} {f' : β → α}
(h : continuous f') (l_inv : left_inverse f f') (r_inv : right_inverse f f') :
is_open_map f :=
of_sections $ λ x, ⟨f', h.continuous_at, r_inv _, l_inv⟩
/-- A continuous surjective open map is a quotient map. -/
lemma to_quotient_map {f : α → β}
(open_map : is_open_map f) (cont : continuous f) (surj : surjective f) :
quotient_map f :=
quotient_map_iff.2 ⟨surj, λ s, ⟨λ h, h.preimage cont, λ h, surj.image_preimage s ▸ open_map _ h⟩⟩
lemma interior_preimage_subset_preimage_interior (hf : is_open_map f) {s : set β} :
interior (f⁻¹' s) ⊆ f⁻¹' (interior s) :=
hf.maps_to_interior (maps_to_preimage _ _)
lemma preimage_interior_eq_interior_preimage (hf₁ : is_open_map f) (hf₂ : continuous f)
(s : set β) :
f⁻¹' (interior s) = interior (f⁻¹' s) :=
subset.antisymm
(preimage_interior_subset_interior_preimage hf₂)
(interior_preimage_subset_preimage_interior hf₁)
lemma preimage_closure_subset_closure_preimage (hf : is_open_map f) {s : set β} :
f ⁻¹' (closure s) ⊆ closure (f ⁻¹' s) :=
begin
rw ← compl_subset_compl,
simp only [← interior_compl, ← preimage_compl, hf.interior_preimage_subset_preimage_interior]
end
lemma preimage_closure_eq_closure_preimage (hf : is_open_map f) (hfc : continuous f) (s : set β) :
f ⁻¹' (closure s) = closure (f ⁻¹' s) :=
hf.preimage_closure_subset_closure_preimage.antisymm (hfc.closure_preimage_subset s)
lemma preimage_frontier_subset_frontier_preimage (hf : is_open_map f) {s : set β} :
f ⁻¹' (frontier s) ⊆ frontier (f ⁻¹' s) :=
by simpa only [frontier_eq_closure_inter_closure, preimage_inter]
using inter_subset_inter hf.preimage_closure_subset_closure_preimage
hf.preimage_closure_subset_closure_preimage
lemma preimage_frontier_eq_frontier_preimage (hf : is_open_map f) (hfc : continuous f) (s : set β) :
f ⁻¹' (frontier s) = frontier (f ⁻¹' s) :=
by simp only [frontier_eq_closure_inter_closure, preimage_inter, preimage_compl,
hf.preimage_closure_eq_closure_preimage hfc]
end is_open_map
lemma is_open_map_iff_nhds_le [topological_space α] [topological_space β] {f : α → β} :
is_open_map f ↔ ∀(a:α), 𝓝 (f a) ≤ (𝓝 a).map f :=
⟨λ hf, hf.nhds_le, is_open_map.of_nhds_le⟩
lemma is_open_map_iff_interior [topological_space α] [topological_space β] {f : α → β} :
is_open_map f ↔ ∀ s, f '' (interior s) ⊆ interior (f '' s) :=
⟨is_open_map.image_interior_subset, λ hs u hu, subset_interior_iff_open.mp $
calc f '' u = f '' (interior u) : by rw hu.interior_eq
... ⊆ interior (f '' u) : hs u⟩
/-- An inducing map with an open range is an open map. -/
protected lemma inducing.is_open_map [topological_space α] [topological_space β] {f : α → β}
(hi : inducing f) (ho : is_open (range f)) :
is_open_map f :=
is_open_map.of_nhds_le $ λ x, (hi.map_nhds_of_mem _ $ is_open.mem_nhds ho $ mem_range_self _).ge
section is_closed_map
variables [topological_space α] [topological_space β]
/-- A map `f : α → β` is said to be a *closed map*, if the image of any closed `U : set α`
is closed in `β`. -/
def is_closed_map (f : α → β) := ∀ U : set α, is_closed U → is_closed (f '' U)
end is_closed_map
namespace is_closed_map
variables [topological_space α] [topological_space β] [topological_space γ]
open function
protected lemma id : is_closed_map (@id α) := assume s hs, by rwa image_id
protected lemma comp {g : β → γ} {f : α → β} (hg : is_closed_map g) (hf : is_closed_map f) :
is_closed_map (g ∘ f) :=
by { intros s hs, rw image_comp, exact hg _ (hf _ hs) }
lemma closure_image_subset {f : α → β} (hf : is_closed_map f) (s : set α) :
closure (f '' s) ⊆ f '' closure s :=
closure_minimal (image_subset _ subset_closure) (hf _ is_closed_closure)
lemma of_inverse {f : α → β} {f' : β → α}
(h : continuous f') (l_inv : left_inverse f f') (r_inv : right_inverse f f') :
is_closed_map f :=
assume s hs,
have f' ⁻¹' s = f '' s, by ext x; simp [mem_image_iff_of_inverse r_inv l_inv],
this ▸ hs.preimage h
lemma of_nonempty {f : α → β} (h : ∀ s, is_closed s → s.nonempty → is_closed (f '' s)) :
is_closed_map f :=
begin
intros s hs, cases eq_empty_or_nonempty s with h2s h2s,
{ simp_rw [h2s, image_empty, is_closed_empty] },
{ exact h s hs h2s }
end
lemma closed_range {f : α → β} (hf : is_closed_map f) : is_closed (range f) :=
@image_univ _ _ f ▸ hf _ is_closed_univ
end is_closed_map
lemma inducing.is_closed_map [topological_space α] [topological_space β]
{f : α → β} (hf : inducing f) (h : is_closed (range f)) : is_closed_map f :=
begin
intros s hs,
rcases hf.is_closed_iff.1 hs with ⟨t, ht, rfl⟩,
rw image_preimage_eq_inter_range,
exact ht.inter h
end
lemma is_closed_map_iff_closure_image [topological_space α] [topological_space β] {f : α → β} :
is_closed_map f ↔ ∀ s, closure (f '' s) ⊆ f '' closure s :=
⟨is_closed_map.closure_image_subset, λ hs c hc, is_closed_of_closure_subset $
calc closure (f '' c) ⊆ f '' (closure c) : hs c
... = f '' c : by rw hc.closure_eq⟩
section open_embedding
variables [topological_space α] [topological_space β] [topological_space γ]
/-- An open embedding is an embedding with open image. -/
@[mk_iff]
structure open_embedding (f : α → β) extends _root_.embedding f : Prop :=
(open_range : is_open $ range f)
lemma open_embedding.is_open_map {f : α → β} (hf : open_embedding f) : is_open_map f :=
hf.to_embedding.to_inducing.is_open_map hf.open_range
lemma open_embedding.map_nhds_eq {f : α → β} (hf : open_embedding f) (a : α) :
map f (𝓝 a) = 𝓝 (f a) :=
hf.to_embedding.map_nhds_of_mem _ $ hf.open_range.mem_nhds $ mem_range_self _
lemma open_embedding.open_iff_image_open {f : α → β} (hf : open_embedding f)
{s : set α} : is_open s ↔ is_open (f '' s) :=
⟨hf.is_open_map s,
λ h, begin
convert ← h.preimage hf.to_embedding.continuous,
apply preimage_image_eq _ hf.inj
end⟩
lemma open_embedding.tendsto_nhds_iff {ι : Type*}
{f : ι → β} {g : β → γ} {a : filter ι} {b : β} (hg : open_embedding g) :
tendsto f a (𝓝 b) ↔ tendsto (g ∘ f) a (𝓝 (g b)) :=
hg.to_embedding.tendsto_nhds_iff
lemma open_embedding.continuous {f : α → β} (hf : open_embedding f) : continuous f :=
hf.to_embedding.continuous
lemma open_embedding.open_iff_preimage_open {f : α → β} (hf : open_embedding f)
{s : set β} (hs : s ⊆ range f) : is_open s ↔ is_open (f ⁻¹' s) :=
begin
convert ←hf.open_iff_image_open.symm,
rwa [image_preimage_eq_inter_range, inter_eq_self_of_subset_left]
end
lemma open_embedding_of_embedding_open {f : α → β} (h₁ : embedding f)
(h₂ : is_open_map f) : open_embedding f :=
⟨h₁, h₂.is_open_range⟩
lemma open_embedding_iff_embedding_open {f : α → β} :
open_embedding f ↔ embedding f ∧ is_open_map f :=
⟨λ h, ⟨h.1, h.is_open_map⟩, λ h, open_embedding_of_embedding_open h.1 h.2⟩
lemma open_embedding_of_continuous_injective_open {f : α → β} (h₁ : continuous f)
(h₂ : injective f) (h₃ : is_open_map f) : open_embedding f :=
begin
simp only [open_embedding_iff_embedding_open, embedding_iff, inducing_iff_nhds, *, and_true],
exact λ a, le_antisymm (h₁.tendsto _).le_comap
(@comap_map _ _ (𝓝 a) _ h₂ ▸ comap_mono (h₃.nhds_le _))
end
lemma open_embedding_iff_continuous_injective_open {f : α → β} :
open_embedding f ↔ continuous f ∧ injective f ∧ is_open_map f :=
⟨λ h, ⟨h.continuous, h.inj, h.is_open_map⟩,
λ h, open_embedding_of_continuous_injective_open h.1 h.2.1 h.2.2⟩
lemma open_embedding_id : open_embedding (@id α) :=
⟨embedding_id, is_open_map.id.is_open_range⟩
lemma open_embedding.comp {g : β → γ} {f : α → β}
(hg : open_embedding g) (hf : open_embedding f) : open_embedding (g ∘ f) :=
⟨hg.1.comp hf.1, (hg.is_open_map.comp hf.is_open_map).is_open_range⟩
lemma open_embedding.is_open_map_iff {g : β → γ} {f : α → β} (hg : open_embedding g) :
is_open_map f ↔ is_open_map (g ∘ f) :=
by simp only [is_open_map_iff_nhds_le, ← @map_map _ _ _ _ f g, ← hg.map_nhds_eq,
map_le_map_iff hg.inj]
lemma open_embedding.of_comp_iff (f : α → β) {g : β → γ} (hg : open_embedding g) :
open_embedding (g ∘ f) ↔ open_embedding f :=
by simp only [open_embedding_iff_continuous_injective_open, ← hg.is_open_map_iff,
← hg.1.continuous_iff, hg.inj.of_comp_iff]
lemma open_embedding.of_comp (f : α → β) {g : β → γ} (hg : open_embedding g)
(h : open_embedding (g ∘ f)) : open_embedding f :=
(open_embedding.of_comp_iff f hg).1 h
end open_embedding
section closed_embedding
variables [topological_space α] [topological_space β] [topological_space γ]
/-- A closed embedding is an embedding with closed image. -/
@[mk_iff]
structure closed_embedding (f : α → β) extends _root_.embedding f : Prop :=
(closed_range : is_closed $ range f)
variables {f : α → β}
lemma closed_embedding.tendsto_nhds_iff {ι : Type*}
{g : ι → α} {a : filter ι} {b : α} (hf : closed_embedding f) :
tendsto g a (𝓝 b) ↔ tendsto (f ∘ g) a (𝓝 (f b)) :=
hf.to_embedding.tendsto_nhds_iff
lemma closed_embedding.continuous (hf : closed_embedding f) : continuous f :=
hf.to_embedding.continuous
lemma closed_embedding.is_closed_map (hf : closed_embedding f) : is_closed_map f :=
hf.to_embedding.to_inducing.is_closed_map hf.closed_range
lemma closed_embedding.closed_iff_image_closed (hf : closed_embedding f)
{s : set α} : is_closed s ↔ is_closed (f '' s) :=
⟨hf.is_closed_map s,
λ h, begin
convert ←continuous_iff_is_closed.mp hf.continuous _ h,
apply preimage_image_eq _ hf.inj
end⟩
lemma closed_embedding.closed_iff_preimage_closed (hf : closed_embedding f)
{s : set β} (hs : s ⊆ range f) : is_closed s ↔ is_closed (f ⁻¹' s) :=
begin
convert ←hf.closed_iff_image_closed.symm,
rwa [image_preimage_eq_inter_range, inter_eq_self_of_subset_left]
end
lemma closed_embedding_of_embedding_closed (h₁ : embedding f)
(h₂ : is_closed_map f) : closed_embedding f :=
⟨h₁, by convert h₂ univ is_closed_univ; simp⟩
lemma closed_embedding_of_continuous_injective_closed (h₁ : continuous f)
(h₂ : injective f) (h₃ : is_closed_map f) : closed_embedding f :=
begin
refine closed_embedding_of_embedding_closed ⟨⟨_⟩, h₂⟩ h₃,
apply le_antisymm (continuous_iff_le_induced.mp h₁) _,
intro s',
change is_open _ ≤ is_open _,
rw [←is_closed_compl_iff, ←is_closed_compl_iff],
generalize : s'ᶜ = s,
rw is_closed_induced_iff,
refine λ hs, ⟨f '' s, h₃ s hs, _⟩,
rw preimage_image_eq _ h₂
end
lemma closed_embedding_id : closed_embedding (@id α) :=
⟨embedding_id, by convert is_closed_univ; apply range_id⟩
lemma closed_embedding.comp {g : β → γ} {f : α → β}
(hg : closed_embedding g) (hf : closed_embedding f) : closed_embedding (g ∘ f) :=
⟨hg.to_embedding.comp hf.to_embedding, show is_closed (range (g ∘ f)),
by rw [range_comp, ←hg.closed_iff_image_closed]; exact hf.closed_range⟩
lemma closed_embedding.closure_image_eq {f : α → β} (hf : closed_embedding f) (s : set α) :
closure (f '' s) = f '' closure s :=
le_antisymm (is_closed_map_iff_closure_image.mp hf.is_closed_map _)
(image_closure_subset_closure_image hf.continuous)
end closed_embedding
|