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affeldt-aist committed Oct 26, 2024
1 parent 46d6b9a commit 8800112
Showing 1 changed file with 4 additions and 4 deletions.
8 changes: 4 additions & 4 deletions theories/separation_axioms.v
Original file line number Diff line number Diff line change
Expand Up @@ -488,7 +488,7 @@ by apply/closure_subset/disjoints_subset; rewrite setIC.
Qed.

Lemma compact_normal_local (K : set T) : hausdorff_space T -> compact K ->
forall A : set T, A `<=` interior K -> {for A, normal_space}.
forall A : set T, A `<=` K^° -> {for A, normal_space}.
Proof.
move=> hT cptV A AK clA B snAB; have /compact_near_coveringP cvA : compact A.
apply/(subclosed_compact clA cptV)/(subset_trans AK).
Expand All @@ -504,7 +504,7 @@ have PsnA : ProperFilter (filter_from (set_nbhs (~` B)) closure).
pose F := powerset_filter_from (filter_from (set_nbhs (~` B)) closure).
have PF : Filter F by exact: powerset_filter_from_filter.
have cvP (x : T) : A x -> \forall x' \near x & i \near F, (~` i) x'.
move=> Ax; case/set_nbhsP: snAB => C [oC AC CB].
move=> Ax; case/set_nbhsP : snAB => C [oC AC CB].
have [] := @compact_regular x _ hT cptV _ C; first exact: AK.
by rewrite nbhsE /=; exists C => //; split => //; exact: AC.
move=> D /nbhs_interior nD cDC.
Expand All @@ -514,12 +514,12 @@ have cvP (x : T) : A x -> \forall x' \near x & i \near F, (~` i) x'.
apply: open_nbhs_nbhs; split; first exact/closed_openC/closed_closure.
exact/(subsetC _ nBZ)/(subset_trans cDC).
by have := @closed_closure _ (~` closure D); rewrite closure_id => <-.
near=> y U => /=; have Dy : interior D y by exact: (near nD _).
near=> y U => /=; have Dy : D^° y by exact: (near nD _).
have UclD : U `<=` closure (~` closure D).
exact: (near (small_set_sub snBD) U).
move=> Uy; have [z [/= + Dz]] := UclD _ Uy _ Dy.
by apply; exact: subset_closure.
case/(_ _ _ _ _ cvP): cvA => R /= [RA Rmono [U RU] RBx].
case/(_ _ _ _ _ cvP) : cvA => R /= [RA Rmono [U RU] RBx].
have [V /set_nbhsP [W [oW cBW WV] clVU]] := RA _ RU; exists (~` W).
apply/set_nbhsP; exists (~` closure W); split.
- exact/closed_openC/closed_closure.
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