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affeldt-aist committed Mar 18, 2024
1 parent 6b94f22 commit b8b8627
Showing 1 changed file with 8 additions and 9 deletions.
17 changes: 8 additions & 9 deletions theories/normedtype.v
Original file line number Diff line number Diff line change
Expand Up @@ -3717,29 +3717,28 @@ End normalP.
Section completely_regular.

Definition completely_regular_space {R : realType} {T : topologicalType} :=
forall (a : T) (B : set T), closed B -> ~ B a -> exists (f : T -> R), [/\
forall (a : T) (B : set T), closed B -> ~ B a -> exists f : T -> R, [/\
continuous f,
f a = 0 &
f @` B `<=` [set 1]
].
f @` B `<=` [set 1] ].

Lemma point_uniform_separator {T : uniformType} (x : T) (B : set T) :
closed B -> ~ B x -> uniform_separator [set x] B.
Proof.
move=> clB nBx; have : open (~` B) by rewrite openC.
rewrite openE => /(_ _ nBx); rewrite /interior /= -nbhs_entourageE.
case=> E entE EnB.
pose T' := ([the pseudoMetricType Rdefinitions.R of gauge.type entE]).
pose T' := [the pseudoMetricType Rdefinitions.R of gauge.type entE].
exists (Uniform.class T); exists E; split => //; last by move => ?.
by rewrite -subset0; case => ? w[/=[-> ? ?]]; apply: (EnB w).
by rewrite -subset0 => -[? w [/= [-> ? ?]]]; exact: (EnB w).
Qed.

Lemma uniform_completely_regular {R : realType} {T : uniformType} :
@completely_regular_space R T.
Lemma uniform_completely_regular {R : realType} {T : uniformType} :
@completely_regular_space R T.
Proof.
move=> x B clB Bx.
move=> x B clB Bx.
have /(@uniform_separatorP _ R) [f] := point_uniform_separator clB Bx.
by case=> ? _; rewrite image_set1 => fx ?; exists f; split => //; apply: fx.
by case=> ? _; rewrite image_set1 => fx ?; exists f; split => //; exact: fx.
Qed.

End completely_regular.
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