let TM be metrizable TopSpace; for Null being Subset of TM st TM | Null is second-countable holds
( ( Null is finite-ind & ind Null <= 0 ) iff for p being Point of TM
for U being open Subset of TM st p in U holds
ex W being open Subset of TM st
( p in W & W c= U & Null misses Fr W ) )
let Null be Subset of TM; ( TM | Null is second-countable implies ( ( Null is finite-ind & ind Null <= 0 ) iff for p being Point of TM
for U being open Subset of TM st p in U holds
ex W being open Subset of TM st
( p in W & W c= U & Null misses Fr W ) ) )
assume A1:
TM | Null is second-countable
; ( ( Null is finite-ind & ind Null <= 0 ) iff for p being Point of TM
for U being open Subset of TM st p in U holds
ex W being open Subset of TM st
( p in W & W c= U & Null misses Fr W ) )
hereby ( ( for p being Point of TM
for U being open Subset of TM st p in U holds
ex W being open Subset of TM st
( p in W & W c= U & Null misses Fr W ) ) implies ( Null is finite-ind & ind Null <= 0 ) )
assume A2:
(
Null is
finite-ind &
ind Null <= 0 )
;
for p being Point of TM
for U being open Subset of TM st p in U holds
ex W being open Subset of TM st
( p in W & W c= U & Null misses Fr W )let p be
Point of
TM;
for U being open Subset of TM st p in U holds
ex W being open Subset of TM st
( p in W & W c= U & Null misses Fr W )let U be
open Subset of
TM;
( p in U implies ex W being open Subset of TM st
( p in W & W c= U & Null misses Fr W ) )assume A3:
p in U
;
ex W being open Subset of TM st
( p in W & W c= U & Null misses Fr W )reconsider P =
{p} as
Subset of
TM by A3, ZFMISC_1:31;
not
p in U `
by A3, XBOOLE_0:def 5;
then A4:
P misses U `
by ZFMISC_1:50;
not
TM is
empty
by A3;
then consider L being
Subset of
TM such that A5:
L separates P,
U `
and A6:
L misses Null
by A1, A2, A4, Th37;
consider W,
W1 being
open Subset of
TM such that A7:
P c= W
and A8:
U ` c= W1
and A9:
W misses W1
and A10:
L = (W \/ W1) `
by A5, METRIZTS:def 3;
take W =
W;
( p in W & W c= U & Null misses Fr W )
(
W c= W1 ` &
W1 ` c= (U `) ` )
by A8, A9, SUBSET_1:12, SUBSET_1:23;
hence
(
p in W &
W c= U )
by A7, ZFMISC_1:31;
Null misses Fr Wthus
Null misses Fr W
verum
end;
set TN = TM | Null;
assume A15:
for p being Point of TM
for U being open Subset of TM st p in U holds
ex W being open Subset of TM st
( p in W & W c= U & Null misses Fr W )
; ( Null is finite-ind & ind Null <= 0 )
A16:
for p being Point of (TM | Null)
for U being open Subset of (TM | Null) st p in U holds
ex W being open Subset of (TM | Null) st
( p in W & W c= U & Fr W is finite-ind & ind (Fr W) <= 0 - 1 )
then A24:
TM | Null is finite-ind
by Th15;
then A25:
Null is finite-ind
by Th18;
ind (TM | Null) <= 0
by A16, A24, Th16;
hence
( Null is finite-ind & ind Null <= 0 )
by A25, Lm5; verum