let TS be TopSpace; :: thesis: ( TS is Hausdorff implies for A being Subset of TS st A <> {} & A is compact holds
for p being Point of TS st p in A ` holds
ex PS, QS being Subset of TS st
( PS is open & QS is open & p in PS & A c= QS & PS misses QS ) )
assume A1:
TS is Hausdorff
; :: thesis: for A being Subset of TS st A <> {} & A is compact holds
for p being Point of TS st p in A ` holds
ex PS, QS being Subset of TS st
( PS is open & QS is open & p in PS & A c= QS & PS misses QS )
let F be Subset of TS; :: thesis: ( F <> {} & F is compact implies for p being Point of TS st p in F ` holds
ex PS, QS being Subset of TS st
( PS is open & QS is open & p in PS & F c= QS & PS misses QS ) )
assume that
A2:
F <> {}
and
A3:
F is compact
; :: thesis: for p being Point of TS st p in F ` holds
ex PS, QS being Subset of TS st
( PS is open & QS is open & p in PS & F c= QS & PS misses QS )
let a be Point of TS; :: thesis: ( a in F ` implies ex PS, QS being Subset of TS st
( PS is open & QS is open & a in PS & F c= QS & PS misses QS ) )
assume A4:
a in F `
; :: thesis: ex PS, QS being Subset of TS st
( PS is open & QS is open & a in PS & F c= QS & PS misses QS )
A5:
not a in F
by A4, XBOOLE_0:def 5;
defpred S1[ set , set , set ] means ex PS, QS being Subset of TS st
( $2 = PS & $3 = QS & PS is open & QS is open & a in PS & $1 in QS & PS /\ QS = {} );
A6:
for x being set st x in F holds
ex y, z being set st
( y in the topology of TS & z in the topology of TS & S1[x,y,z] )
proof
let x be
set ;
:: thesis: ( x in F implies ex y, z being set st
( y in the topology of TS & z in the topology of TS & S1[x,y,z] ) )
assume A7:
x in F
;
:: thesis: ex y, z being set st
( y in the topology of TS & z in the topology of TS & S1[x,y,z] )
then reconsider p =
x as
Point of
TS ;
consider W,
V being
Subset of
TS such that A8:
W is
open
and A9:
V is
open
and A10:
a in W
and A11:
p in V
and A12:
W misses V
by A1, A5, A7, PRE_TOPC:def 16;
reconsider PS =
W,
QS =
V as
set ;
take
PS
;
:: thesis: ex z being set st
( PS in the topology of TS & z in the topology of TS & S1[x,PS,z] )
take
QS
;
:: thesis: ( PS in the topology of TS & QS in the topology of TS & S1[x,PS,QS] )
thus
(
PS in the
topology of
TS &
QS in the
topology of
TS )
by A8, A9, PRE_TOPC:def 5;
:: thesis: S1[x,PS,QS]
take
W
;
:: thesis: ex QS being Subset of TS st
( PS = W & QS = QS & W is open & QS is open & a in W & x in QS & W /\ QS = {} )
take
V
;
:: thesis: ( PS = W & QS = V & W is open & V is open & a in W & x in V & W /\ V = {} )
thus
(
PS = W &
QS = V &
W is
open &
V is
open &
a in W &
x in V &
W /\ V = {} )
by A8, A9, A10, A11, A12, XBOOLE_0:def 7;
:: thesis: verum
end;
consider f, g being Function such that
A13:
( dom f = F & dom g = F )
and
A14:
for x being set st x in F holds
S1[x,f . x,g . x]
from WELLORD2:sch 2(A6);
g .: F c= bool the carrier of TS
then reconsider C = g .: F as Subset-Family of TS ;
F c= union C
then A20:
C is Cover of F
by SETFAM_1:def 12;
A21:
C is open
then consider C' being Subset-Family of TS such that
A24:
C' c= C
and
A25:
C' is Cover of F
and
A26:
C' is finite
by A3, A20, Def7;
C' c= rng g
by A13, A24, RELAT_1:146;
then consider H' being set such that
A27:
H' c= dom g
and
A28:
H' is finite
and
A29:
g .: H' = C'
by A26, ORDERS_1:195;
f .: H' c= bool the carrier of TS
then reconsider B = f .: H' as Subset-Family of TS ;
take G0 = meet B; :: thesis: ex QS being Subset of TS st
( G0 is open & QS is open & a in G0 & F c= QS & G0 misses QS )
take G1 = union C'; :: thesis: ( G0 is open & G1 is open & a in G0 & F c= G1 & G0 misses G1 )
B is open
hence
G0 is open
by A28, TOPS_2:27; :: thesis: ( G1 is open & a in G0 & F c= G1 & G0 misses G1 )
thus
G1 is open
by A21, A24, TOPS_2:18, TOPS_2:26; :: thesis: ( a in G0 & F c= G1 & G0 misses G1 )
consider z being Element of F;
F c= union C'
by A25, SETFAM_1:def 12;
then
z in union C'
by A2, TARSKI:def 3;
then consider D being set such that
z in D
and
A35:
D in C'
by TARSKI:def 4;
reconsider D' = D as Subset of TS by A35;
consider y being set such that
A36:
y in dom g
and
A37:
y in H'
and
D' = g . y
by A29, A35, FUNCT_1:def 12;
consider PS, QS being Subset of TS such that
A38:
f . y = PS
and
g . y = QS
and
PS is open
and
QS is open
and
a in PS
and
y in QS
and
PS /\ QS = {}
by A13, A14, A36;
A39:
B <> {}
by A13, A36, A37, A38, FUNCT_1:def 12;
for G being set st G in B holds
a in G
hence
a in G0
by A39, SETFAM_1:def 1; :: thesis: ( F c= G1 & G0 misses G1 )
thus
F c= G1
by A25, SETFAM_1:def 12; :: thesis: G0 misses G1
thus
G0 /\ G1 = {}
:: according to XBOOLE_0:def 7 :: thesis: verumproof
assume A43:
G0 /\ G1 <> {}
;
:: thesis: contradiction
consider x being
Element of
(meet B) /\ (union C');
A44:
(
x in union C' &
x in meet B )
by A43, XBOOLE_0:def 4;
then consider A being
set such that A45:
x in A
and A46:
A in C'
by TARSKI:def 4;
consider z being
set such that A47:
z in dom g
and A48:
z in H'
and A49:
A = g . z
by A29, A46, FUNCT_1:def 12;
consider PS,
QS being
Subset of
TS such that A50:
f . z = PS
and A51:
g . z = QS
and
PS is
open
and
QS is
open
and
a in PS
and
z in QS
and A52:
PS /\ QS = {}
by A13, A14, A47;
PS in B
by A13, A47, A48, A50, FUNCT_1:def 12;
then
(
x in QS &
x in PS )
by A44, A45, A49, A51, SETFAM_1:def 1;
hence
contradiction
by A52, XBOOLE_0:def 4;
:: thesis: verum
end;