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Porting note: added proof #10888

@pitmonticone

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@pitmonticone

Classifies porting notes claiming added proof.

Examples

/-- In a paracompact space, every open covering of a closed set admits a locally finite refinement
indexed by the same type. -/
theorem precise_refinement_set [ParacompactSpace X] {s : Set X} (hs : IsClosed s) (u : ι → Set X)
(uo : ∀ i, IsOpen (u i)) (us : s ⊆ ⋃ i, u i) :
∃ v : ι → Set X, (∀ i, IsOpen (v i)) ∧ (s ⊆ ⋃ i, v i) ∧ LocallyFinite v ∧ ∀ i, v i ⊆ u i := by
-- Porting note: Added proof of uc
have uc : (iUnion fun i => Option.elim' sᶜ u i) = univ := by
apply Subset.antisymm (subset_univ _)
· simp_rw [← compl_union_self s, Option.elim', iUnion_option]
apply union_subset_union_right sᶜ us
rcases precise_refinement (Option.elim' sᶜ u) (Option.forall.2 ⟨isOpen_compl_iff.2 hs, uo⟩)
uc with
⟨v, vo, vc, vf, vu⟩
refine' ⟨v ∘ some, fun i ↦ vo _, _, vf.comp_injective (Option.some_injective _), fun i ↦ vu _⟩
· simp only [iUnion_option, ← compl_subset_iff_union] at vc
exact Subset.trans (subset_compl_comm.1 <| vu Option.none) vc
#align precise_refinement_set precise_refinement_set

/-- (Impl) A preliminary definition to avoid timeouts. -/
@[simps]
def conesEquivFunctor (B : C) {J : Type w} (F : Discrete J ⥤ Over B) :
Cone (widePullbackDiagramOfDiagramOver B F) ⥤ Cone F where
obj c :=
{ pt := Over.mk (c.π.app none)
π :=
{ app := fun ⟨j⟩ => Over.homMk (c.π.app (some j)) (c.w (WidePullbackShape.Hom.term j))
-- Porting note: Added a proof for `naturality`
naturality := fun ⟨X⟩ ⟨Y⟩ ⟨⟨f⟩⟩ => by dsimp at f ⊢; aesop_cat } }

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