let T be non empty TopSpace; :: thesis: ( T is T_2 & T is paracompact implies T is normal )
assume A1:
( T is T_2 & T is paracompact )
; :: thesis: T is normal
for A, B being Subset of T st A <> {} & B <> {} & A is closed & B is closed & A misses B holds
ex W, V being Subset of T st
( W is open & V is open & A c= W & B c= V & W misses V )
proof
let A,
B be
Subset of
T;
:: thesis: ( A <> {} & B <> {} & A is closed & B is closed & A misses B implies ex W, V being Subset of T st
( W is open & V is open & A c= W & B c= V & W misses V ) )
assume that A2:
A <> {}
and
B <> {}
and A3:
A is
closed
and A4:
B is
closed
and A5:
A misses B
;
:: thesis: ex W, V being Subset of T st
( W is open & V is open & A c= W & B c= V & W misses V )
for
x being
Point of
T st
x in B holds
ex
W,
V being
Subset of
T st
(
W is
open &
V is
open &
A c= W &
x in V &
W misses V )
proof
let x be
Point of
T;
:: thesis: ( x in B implies ex W, V being Subset of T st
( W is open & V is open & A c= W & x in V & W misses V ) )
assume
x in B
;
:: thesis: ex W, V being Subset of T st
( W is open & V is open & A c= W & x in V & W misses V )
then
not
x in A
by A5, XBOOLE_0:3;
then A6:
x in A `
by SUBSET_1:50;
T is
regular
by A1, Th27;
then consider V,
W being
Subset of
T such that A7:
V is
open
and A8:
W is
open
and A9:
x in V
and A10:
A c= W
and A11:
V misses W
by A2, A3, A6, COMPTS_1:def 5;
take
W
;
:: thesis: ex V being Subset of T st
( W is open & V is open & A c= W & x in V & W misses V )
take
V
;
:: thesis: ( W is open & V is open & A c= W & x in V & W misses V )
thus
(
W is
open &
V is
open &
A c= W &
x in V &
W misses V )
by A7, A8, A9, A10, A11;
:: thesis: verum
end;
then consider Y,
Z being
Subset of
T such that A12:
(
Y is
open &
Z is
open &
A c= Y &
B c= Z &
Y misses Z )
by A1, A3, A4, A5, Th26;
take
Y
;
:: thesis: ex V being Subset of T st
( Y is open & V is open & A c= Y & B c= V & Y misses V )
take
Z
;
:: thesis: ( Y is open & Z is open & A c= Y & B c= Z & Y misses Z )
thus
(
Y is
open &
Z is
open &
A c= Y &
B c= Z &
Y misses Z )
by A12;
:: thesis: verum
end;
hence
T is normal
by COMPTS_1:def 6; :: thesis: verum