let TS be TopSpace; ( TS is T_2 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 T_2
; 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; ( 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
; 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 )
set z = the Element of F;
let a be Point of TS; ( 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
a in F `
; ex PS, QS being Subset of TS st
( PS is open & QS is open & a in PS & F c= QS & PS misses QS )
then A4:
not a in F
by XBOOLE_0:def 5;
defpred S1[ object , object , object ] 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 = {} );
A5:
for x being object st x in F holds
ex y, z being object st
( y in the topology of TS & z in the topology of TS & S1[x,y,z] )
proof
let x be
object ;
( x in F implies ex y, z being object st
( y in the topology of TS & z in the topology of TS & S1[x,y,z] ) )
assume A6:
x in F
;
ex y, z being object 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 A7:
W is
open
and A8:
V is
open
and A9:
a in W
and A10:
p in V
and A11:
W misses V
by A1, A4, A6;
reconsider PS =
W,
QS =
V as
set ;
take
PS
;
ex z being object st
( PS in the topology of TS & z in the topology of TS & S1[x,PS,z] )
take
QS
;
( 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 A7, A8;
S1[x,PS,QS]
take
W
;
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
;
( 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 A7, A8, A9, A10, A11;
verum
end;
consider f, g being Function such that
A12:
( dom f = F & dom g = F )
and
A13:
for x being object st x in F holds
S1[x,f . x,g . x]
from MCART_1:sch 1(A5);
g .: F c= bool the carrier of TS
then reconsider C = g .: F as Subset-Family of TS ;
A16:
C is open
F c= union C
then
C is Cover of F
by SETFAM_1:def 11;
then consider C9 being Subset-Family of TS such that
A22:
C9 c= C
and
A23:
C9 is Cover of F
and
A24:
C9 is finite
by A3, A16;
C9 c= rng g
by A12, A22, RELAT_1:113;
then consider H9 being set such that
A25:
H9 c= dom g
and
A26:
H9 is finite
and
A27:
g .: H9 = C9
by A24, ORDERS_1:85;
f .: H9 c= bool the carrier of TS
then reconsider B = f .: H9 as Subset-Family of TS ;
take G0 = meet B; 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 C9; ( G0 is open & G1 is open & a in G0 & F c= G1 & G0 misses G1 )
B is open
hence
G0 is open
by A26, TOPS_2:20; ( G1 is open & a in G0 & F c= G1 & G0 misses G1 )
thus
G1 is open
by A16, A22, TOPS_2:11, TOPS_2:19; ( a in G0 & F c= G1 & G0 misses G1 )
A32:
for G being set st G in B holds
a in G
F c= union C9
by A23, SETFAM_1:def 11;
then
the Element of F in union C9
by A2;
then consider D being set such that
the Element of F in D
and
A36:
D in C9
by TARSKI:def 4;
reconsider D9 = D as Subset of TS by A36;
consider y being object such that
A37:
y in dom g
and
A38:
y in H9
and
D9 = g . y
by A27, A36, FUNCT_1:def 6;
ex PS, QS being Subset of TS st
( f . y = PS & g . y = QS & PS is open & QS is open & a in PS & y in QS & PS /\ QS = {} )
by A12, A13, A37;
then
B <> {}
by A12, A37, A38, FUNCT_1:def 6;
hence
a in G0
by A32, SETFAM_1:def 1; ( F c= G1 & G0 misses G1 )
thus
F c= G1
by A23, SETFAM_1:def 11; G0 misses G1
thus
G0 /\ G1 = {}
XBOOLE_0:def 7 verumproof
set x = the
Element of
(meet B) /\ (union C9);
assume A39:
G0 /\ G1 <> {}
;
contradiction
then A40:
the
Element of
(meet B) /\ (union C9) in meet B
by XBOOLE_0:def 4;
the
Element of
(meet B) /\ (union C9) in union C9
by A39, XBOOLE_0:def 4;
then consider A being
set such that A41:
the
Element of
(meet B) /\ (union C9) in A
and A42:
A in C9
by TARSKI:def 4;
consider z being
object such that A43:
z in dom g
and A44:
z in H9
and A45:
A = g . z
by A27, A42, FUNCT_1:def 6;
consider PS,
QS being
Subset of
TS such that A46:
f . z = PS
and A47:
g . z = QS
and
PS is
open
and
QS is
open
and
a in PS
and
z in QS
and A48:
PS /\ QS = {}
by A12, A13, A43;
PS in B
by A12, A43, A44, A46, FUNCT_1:def 6;
then
the
Element of
(meet B) /\ (union C9) in PS
by A40, SETFAM_1:def 1;
hence
contradiction
by A41, A45, A47, A48, XBOOLE_0:def 4;
verum
end;