Datasets:
Tasks:
Text Generation
Modalities:
Text
Sub-tasks:
language-modeling
Languages:
English
Size:
100K - 1M
License:
/- | |
Copyright (c) 2022 Yury Kudryashov. All rights reserved. | |
Released under Apache 2.0 license as described in the file LICENSE. | |
Authors: Yury Kudryashov | |
-/ | |
import analysis.convex.star | |
import topology.homotopy.contractible | |
/-! | |
# A convex set is contractible | |
In this file we prove that a (star) convex set in a real topological vector space is a contractible | |
topological space. | |
-/ | |
variables {E : Type*} [add_comm_group E] [module ℝ E] [topological_space E] | |
[has_continuous_add E] [has_continuous_smul ℝ E] {s : set E} {x : E} | |
/-- A non-empty star convex set is a contractible space. -/ | |
protected lemma star_convex.contractible_space (h : star_convex ℝ x s) (hne : s.nonempty) : | |
contractible_space s := | |
begin | |
refine (contractible_iff_id_nullhomotopic _).2 ⟨⟨x, h.mem hne⟩, | |
⟨⟨⟨λ p, ⟨p.1.1 • x + (1 - p.1.1) • p.2, _⟩, _⟩, λ x, _, λ x, _⟩⟩⟩, | |
{ exact h p.2.2 p.1.2.1 (sub_nonneg.2 p.1.2.2) (add_sub_cancel'_right _ _) }, | |
{ exact continuous_subtype_mk _ | |
(((continuous_subtype_val.comp continuous_fst).smul continuous_const).add | |
((continuous_const.sub $ continuous_subtype_val.comp continuous_fst).smul | |
(continuous_subtype_val.comp continuous_snd))) }, | |
{ ext1, simp }, | |
{ ext1, simp } | |
end | |
/-- A non-empty convex set is a contractible space. -/ | |
protected lemma convex.contractible_space (hs : convex ℝ s) (hne : s.nonempty) : | |
contractible_space s := | |
let ⟨x, hx⟩ := hne in (hs.star_convex hx).contractible_space hne | |
@[priority 100] instance real_topological_vector_space.contractible_space : contractible_space E := | |
(homeomorph.set.univ E).contractible_space_iff.mp $ convex_univ.contractible_space set.univ_nonempty | |