### Connected Spaces

by

Copyright (c) 1989 Association of Mizar Users

MML identifier: CONNSP_1
[ MML identifier index ]

```environ

vocabulary PRE_TOPC, BOOLE, SUBSET_1, RELAT_2, ORDINAL2, RELAT_1, TOPS_1,
SETFAM_1, TARSKI, CONNSP_1;
notation TARSKI, XBOOLE_0, SUBSET_1, FUNCT_1, STRUCT_0, PRE_TOPC, TOPS_1;
constructors TOPS_1, MEMBERED;
clusters PRE_TOPC, RELSET_1, SUBSET_1, MEMBERED, ZFMISC_1;
requirements SUBSET, BOOLE;
definitions XBOOLE_0;
theorems TARSKI, FUNCT_1, FUNCT_2, ZFMISC_1, SETFAM_1, PRE_TOPC, TOPS_1,
SUBSET_1, RELAT_1, XBOOLE_0, XBOOLE_1;
schemes PRE_TOPC;

begin
reserve GX for TopSpace;
reserve A, B, C for Subset of GX;
reserve TS for TopStruct;
reserve K, K1, L, L1 for Subset of TS;

::
::                         Separated sets
::

definition let GX be TopStruct, A,B be Subset of GX;
pred A,B are_separated means
:Def1: Cl A misses B & A misses Cl B;
symmetry;
end;

canceled;

theorem Th2:
K,L are_separated implies K misses L
proof assume
A1:  (Cl K) /\ L = {} & K /\ Cl L = {};
K c= Cl K & L c= L by PRE_TOPC:48;
then K /\ L c= (Cl K) /\ L by XBOOLE_1:27;
hence K /\ L = {} by A1,XBOOLE_1:3;
end;

theorem Th3:
[#]TS = K \/ L & K is closed & L is closed & K misses L
implies K,L are_separated
proof assume that
A1:  [#]TS = K \/ L & K is closed & L is closed and
A2:  K misses L;
A3:   K /\ L = {} by A2,XBOOLE_0:def 7;
(Cl K) /\ L = K /\ L & K /\ Cl L = K /\ L by A1,PRE_TOPC:52;
then (Cl K) misses L & K misses Cl L by A3,XBOOLE_0:def 7;
hence thesis by Def1;
end;

theorem Th4:
[#]GX = A \/ B & A is open & B is open & A misses B
implies A,B are_separated
proof assume that
A1:  [#]GX = A \/ B and
A2:  A is open & B is open and
A3:  A misses B;
A4:  Cl([#]GX \ A) = [#]GX \ A &
Cl([#]GX \ B) = [#]GX \ B by A2,PRE_TOPC:53;
B = [#]GX \ A & A = [#]GX \ B by A1,A3,PRE_TOPC:25;
then B is closed & A is closed by A4,PRE_TOPC:52;
hence A,B are_separated by A1,A3,Th3;
end;

theorem Th5:
[#]GX = A \/ B & A,B are_separated implies
A is open closed & B is open closed
proof assume that
A1:  [#]GX = A \/ B and
A2:  A,B are_separated;
A3: A misses B by A2,Th2;
then A4:  B = [#]GX \ A by A1,PRE_TOPC:25;
A5:  A c= Cl A & B c= Cl B by PRE_TOPC:48;
A6:  Cl([#]GX) =[#]GX by PRE_TOPC:52;
A7:  Cl ( A \/ B ) = Cl A \/ Cl B by PRE_TOPC:50;
A8:  now assume
A9:   (Cl A) misses B;
Cl A c= A \/ B by A1,A6,A7,XBOOLE_1:7;
then Cl A c= A by A9,XBOOLE_1:73;
hence Cl A = A by A5,XBOOLE_0:def 10;
end;
A10: now assume
A11:   A misses Cl B;
Cl B c= A \/ B by A1,A6,A7,XBOOLE_1:7;
then Cl B c= B by A11,XBOOLE_1:73;
hence Cl B = B by A5,XBOOLE_0:def 10;
end;
[#]GX \ B = A by A1,A3,PRE_TOPC:25;
hence A is open closed & B is open closed
by A2,A4,A8,A10,Def1,PRE_TOPC:52,53;
end;

theorem Th6:
for X' being SubSpace of GX, P1,Q1 being Subset of GX,
P,Q being Subset of X' st P=P1 & Q=Q1 holds
P,Q are_separated implies P1,Q1 are_separated
proof
let X' be SubSpace of GX, P1,Q1 be Subset of GX,
P,Q be Subset of X' such that
A1:   P = P1 and
A2:   Q = Q1;
assume A3: (Cl P) /\ Q = {} & P /\ Cl Q = {};
reconsider P2 = P, Q2 = Q as Subset of GX by PRE_TOPC:39;
A4:  (Cl P) /\ Q = ((Cl P2) /\ ([#](X'))) /\ Q by PRE_TOPC:47
.= (Cl P2) /\ (Q /\ [#] X') by XBOOLE_1:16
.= (Cl P2) /\ Q2 by PRE_TOPC:15;
P /\ Cl Q = P /\ (([#] X') /\ Cl Q2) by PRE_TOPC:47
.= P /\ [#] X' /\ Cl Q2 by XBOOLE_1:16
.= P2 /\ Cl Q2 by PRE_TOPC:15;
then (Cl P2) misses Q2 & P2 misses Cl Q2 by A3,A4,XBOOLE_0:def 7;
hence P1,Q1 are_separated by A1,A2,Def1;
end;

theorem Th7:
for X' being SubSpace of GX, P,Q being Subset of GX,
P1,Q1 being Subset of X' st P=P1 & Q=Q1 & P \/ Q c= [#](X')
holds P,Q are_separated implies P1,Q1 are_separated
proof
let X' be SubSpace of GX, P,Q be Subset of GX,
P1,Q1 be Subset of X' such that
A1:  P = P1 and
A2:  Q = Q1 and
A3:  P \/ Q c= [#](X');
assume A4: (Cl P) /\ Q = {} & P /\ Cl Q = {};
P c= P \/ Q & Q c= P \/ Q by XBOOLE_1:7;
then P c= [#](X') & Q c= [#](X') by A3,XBOOLE_1:1;
then reconsider P2 = P, Q2 = Q as Subset of X'
by PRE_TOPC:16;
Cl P2 = (Cl P) /\ [#] X' & Cl Q2 = (Cl Q) /\ [#] X' by PRE_TOPC:47;
then A5:  (Cl P2) /\ Q2 = (Cl P) /\ (Q2 /\ [#] X') by XBOOLE_1:16
.= (Cl P) /\ Q by PRE_TOPC:15;
P2 /\ Cl Q2 = P2 /\ (([#] X') /\ Cl Q) by PRE_TOPC:47
.= (P2 /\ [#] X') /\ Cl Q by XBOOLE_1:16
.= P /\ Cl Q by PRE_TOPC:15;
then (Cl P2) misses Q2 & P2 misses Cl Q2 by A4,A5,XBOOLE_0:def 7;
hence P1,Q1 are_separated by A1,A2,Def1;
end;

theorem Th8:
K,L are_separated & K1 c= K & L1 c= L implies
K1,L1 are_separated
proof assume that
A1:  (Cl K) /\ L = {} & K /\ Cl L = {} and
A2:  K1 c= K and
A3:  L1 c= L;
Cl K1 c= Cl K & Cl L1 c= Cl L by A2,A3,PRE_TOPC:49;
then (Cl K1) /\ L1 c= (Cl K) /\ L & K1 /\ Cl L1 c= K /\ Cl L
by A2,A3,XBOOLE_1:27;
then (Cl K1) /\ L1 = {}TS & K1 /\ Cl L1 = {}TS by A1,XBOOLE_1:3;
then (Cl K1) misses L1 & K1 misses Cl L1 by XBOOLE_0:def 7;
hence K1,L1 are_separated by Def1;
end;

theorem Th9:
A,B are_separated & A,C are_separated implies A,B \/ C are_separated
proof assume that
A1:  (Cl A) misses B & A misses Cl B and
A2:  (Cl A) misses C & A misses Cl C;
A3:   (Cl A) /\ B = {} & A /\ Cl B = {} &
(Cl A) /\ C = {} & A /\ Cl C = {} by A1,A2,XBOOLE_0:def 7;
(Cl A) /\ (B \/ C) = ((Cl A) /\ B) \/ ((Cl A) /\ C) by XBOOLE_1:23
.= {}GX by A3;
then A4:   (Cl A) misses (B \/ C) by XBOOLE_0:def 7;
A /\ Cl (B \/ C) = A /\ ((Cl B) \/ Cl C) by PRE_TOPC:50
.= (A /\ Cl B) \/ (A /\ Cl C) by XBOOLE_1:23
.= {}GX by A3;
then A misses Cl (B \/ C) by XBOOLE_0:def 7;
hence A,B \/ C are_separated by A4,Def1;
end;

theorem Th10:
(K is closed & L is closed) or (K is open & L is open)
implies K \ L,L \ K are_separated
proof assume
A1: (K is closed & L is closed) or (K is open & L is open);
A2:  now
let K,L be Subset of TS such that
A3:   K is open & L is open;
A4:   K \ L = K /\ (L`) & L \ K = L /\ (K`) by SUBSET_1:32;
Cl(K /\ (L`)) c= (Cl K) /\ Cl (L`) & L /\ (K`) c= L /\ (K`)
by PRE_TOPC:51;
then A5:   (Cl(K \ L)) /\ (L \ K) c= ((Cl K) /\ Cl(L`)) /\ (L /\ (K`))
by A4,XBOOLE_1:27;
Cl(L /\ (K`)) c= (Cl L) /\ Cl(K`) & K /\ (L`) c= K /\ (L`)
by PRE_TOPC:51;
then A6:   (K \ L) /\ Cl(L \ K) c= (K /\ (L`)) /\ ((Cl L) /\ Cl(K`))
by A4,XBOOLE_1:27;
A7:  Cl([#]TS \ K) = [#]TS \ K & Cl([#]TS \ L) = [#]TS \ L by A3,PRE_TOPC:53;
A8:   [#]TS \ K = K` & [#]TS \ L = L` by PRE_TOPC:17;
then A9:  ((Cl K) /\ Cl(L`)) /\ (L /\ (K`)) =
((Cl K) /\ (L`)) /\ (L /\ (K`)) by A3,PRE_TOPC:53;
L misses L` & K misses K` by PRE_TOPC:26;
then A10:    L /\ L` = {} & K /\ K` = {} by XBOOLE_0:def 7;
(Cl K) /\ (L`) c= L` & L /\ K` c= L by XBOOLE_1:17;
then ((Cl K) /\ L`) /\ (L /\ K`) c= L /\ (L`) by XBOOLE_1:27;
then A11: (Cl(K \ L)) /\ (L \ K) c= {} by A5,A9,A10,XBOOLE_1:1;
K /\ L` c= K & (Cl L) /\ K` c= K` by XBOOLE_1:17;
then (K /\ (L`)) /\ ((Cl L) /\ Cl(K`)) c= K /\ (K`) by A7,A8,XBOOLE_1:27
;
then (K \ L) /\ Cl(L \ K) c= {} by A6,A10,XBOOLE_1:1;
then (Cl(K \ L)) /\ (L \ K) = {}TS &
(K \ L) /\ Cl(L \ K) = {}TS by A11,XBOOLE_1:3;
then (Cl(K \ L)) misses (L \ K) &
(K \ L) misses Cl(L \ K) by XBOOLE_0:def 7;
hence K \ L,L \ K are_separated by Def1;
end;
now
let K,L be Subset of TS;
assume K is closed & L is closed;
then A12:         [#]TS \ K is open & [#]TS \ L is open by PRE_TOPC:def 6;
A13:  [#]TS \ L = L` & [#]TS \ K = K` by PRE_TOPC:17;
then A14:  ([#]TS \ L) \ ([#]TS \ K) = (L`) /\ (([#]TS \ K)`) by SUBSET_1:
32
.= (L`) /\ ([#]TS \([#]TS \ K)) by PRE_TOPC:17
.= (L`) /\ K by PRE_TOPC:22
.= K \ L by SUBSET_1:32;
([#]TS \ K) \ ([#]TS \ L) = (K`) /\ (([#]TS \ L)`) by A13,SUBSET_1:32
.= (K`) /\ ([#]TS \ ([#]TS \ L)) by PRE_TOPC:17
.= (K`) /\ L by PRE_TOPC:22
.= L \ K by SUBSET_1:32;
hence K \ L,L \ K are_separated by A2,A12,A14;
end;
hence thesis by A1,A2;
end;

::
::                        Connected Spaces
::

definition let GX be TopStruct;
attr GX is connected means
:Def2:for A, B being Subset of GX st
[#]GX = A \/ B & A,B are_separated
holds A = {}GX or B = {}GX;
end;

theorem Th11:
GX is connected iff for A, B being Subset of GX
st [#]GX = A \/ B & A <> {}GX & B <> {}GX & A is closed &
B is closed holds A meets B
proof
A1:  now
given A, B being Subset of GX such that
A2:   [#]GX = A \/ B and
A3:   A <> {}GX & B <> {}GX and
A4:   A is closed & B is closed & A misses B;
A,B are_separated by A2,A4,Th3;
hence not GX is connected by A2,A3,Def2;
end;
now assume not GX is connected;
then consider P, Q being Subset of GX
such that
A5:  [#]GX = P \/ Q and
A6:  P,Q are_separated and
A7:  P <> {}GX & Q <> {}GX by Def2;
reconsider P, Q as Subset of GX;
[#]GX = P \/ Q by A5;
then A8:  P is closed & Q is closed by A6,Th5;
P misses Q by A6,Th2;
hence ex A,B being Subset of GX st [#]GX = A \/ B &
A <> {}GX & B <> {}GX & A is closed & B is closed &
A misses B by A5,A7,A8;
end;
hence thesis by A1;
end;

theorem
GX is connected iff for A,B being Subset of GX
st [#]GX = A \/ B & A <> {}GX & B <> {}GX & A is open &
B is open holds A meets B
proof
A1:  now given A,B being Subset of GX such that
A2:  [#]GX = A \/ B and
A3:  A <> {}GX & B <> {}GX and
A4:  A is open & B is open and
A5:  A misses B;
A,B are_separated by A2,A4,A5,Th4;
hence not GX is connected by A2,A3,Def2;
end;
now assume not GX is connected;
then consider P,Q being Subset of GX
such that
A6:  [#]GX = P \/ Q and
A7:  P,Q are_separated and
A8:  P <> {}GX & Q <> {}GX by Def2;
reconsider P, Q as Subset of GX;
[#]GX = P \/ Q by A6;
then A9:  P is open & Q is open by A7,Th5;
P misses Q by A7,Th2;
hence ex A,B being Subset of GX st [#]GX = A \/ B &
A <> {}GX & B <> {}GX & A is open & B is open &
A misses B by A6,A8,A9;
end;
hence thesis by A1;
end;

theorem Th13:
GX is connected iff for A being Subset of GX st A <> {}GX
& A <> [#]GX holds Cl A meets Cl([#]GX \ A)
proof
A1:  now given A being Subset of GX such that
A2:  A <> {}GX and
A3:  A <> [#]GX and
A4:  (Cl A) misses Cl([#]GX \ A);
A5:   (Cl A) /\ Cl([#]GX \ A) = {} by A4,XBOOLE_0:def 7;
A6:  [#]GX \ A <> {}GX by A3,PRE_TOPC:23;
[#]GX \ A c= Cl([#]GX \ A) &
Cl A c= Cl A by PRE_TOPC:48;
then (Cl A) /\ ([#]GX \ A) c= (Cl A) /\ Cl([#]GX \ A) by XBOOLE_1:27;
then (Cl A) /\ ([#]GX \ A) = {} by A5,XBOOLE_1:3;
then A7: (Cl A) misses ([#]GX \ A) by XBOOLE_0:def 7;
A c= Cl A & Cl ([#]GX \ A) c= Cl([#]GX \ A) by PRE_TOPC:48;
then A /\ Cl([#]GX \ A) c= (Cl A) /\ Cl([#]GX \ A) by XBOOLE_1:27;
then A /\ Cl([#]GX \ A) = {}GX by A5,XBOOLE_1:3;
then A misses Cl([#]GX \ A) by XBOOLE_0:def 7;
then A8:  A,[#]GX \ A are_separated by A7,Def1;
[#]GX = A \/ (A`) by PRE_TOPC:18;
then [#]GX = A \/ ([#]GX \ A) by PRE_TOPC:17;
hence not GX is connected by A2,A6,A8,Def2;
end;
now assume not GX is connected;
then consider A, B being Subset of GX such that
A9:  [#]GX = A \/ B and
A10:   A <> {}GX and
A11:  B <> {}GX and
A12:  A is closed & B is closed and
A13:  A misses B by Th11;
A14:  B = [#]GX \ A by A9,A13,PRE_TOPC:25;
A15:      Cl A = A & Cl B = B by A12,PRE_TOPC:52;
A <> [#]GX by A11,A14,PRE_TOPC:23;
hence ex A being Subset of GX st A <> {}GX &
A <> [#]GX & (Cl A) misses Cl([#]GX \ A) by A10,A13,A14,A15;
end;
hence thesis by A1;
end;

theorem
GX is connected iff for A being Subset of GX st A is open closed holds
A = {}GX or A = [#]GX
proof
A1:   now given A1 being Subset of GX such that
A2:  A1 is open closed & A1 <> {}GX & A1 <> [#]GX;
A3:  Cl A1 = A1 & Cl ([#]GX \ A1) = [#]GX \ A1 by A2,PRE_TOPC:52,53;
A4:   A1 misses A1` by PRE_TOPC:26;
A1 /\ ([#]GX \ A1) = A1 /\ A1` by PRE_TOPC:17;
then (Cl A1) /\ Cl([#]GX \ A1) = {} by A3,A4,XBOOLE_0:def 7;
then (Cl A1) misses Cl([#]GX \ A1) by XBOOLE_0:def 7;
hence not GX is connected by A2,Th13;
end;
now assume not GX is connected;
then consider P,Q being Subset of GX such that
A5:  [#]GX = P \/ Q and
A6:  P,Q are_separated and
A7:  P <> {}GX & Q <> {}GX by Def2;
reconsider P, Q as Subset of GX;
[#]GX = P \/ Q by A5;
then A8:  P is open closed & Q is open closed by A6,Th5;
P misses Q by A6,Th2;
then Q = [#]GX \ P by A5,PRE_TOPC:25;
then P <> [#]GX by A7,PRE_TOPC:23;
hence ex P being Subset of GX st P is open closed &
P <> {}GX & P <> [#]GX by A7,A8;
end;
hence thesis by A1;
end;

theorem
for GY being TopSpace
for F being map of GX,GY st F is continuous
& F.:[#]GX = [#]GY & GX is connected holds GY is connected
proof let GY be TopSpace;
let F be map of GX,GY such that
A1:  F is continuous and
A2:  F.:[#]GX = [#]GY and
A3:  GX is connected;
A4:  the carrier of GY = F.:[#]GX by A2,PRE_TOPC:12
.= F.:(the carrier of GX) by PRE_TOPC:12;
assume not GY is connected;
then consider A, B being Subset of GY such that
A5:  [#]GY = A \/ B and
A6:  A <> {}GY & B <> {}GY and
A7:  A is closed & B is closed and
A8:  A misses B by Th11;
A9:  A /\ B = {} by A8,XBOOLE_0:def 7;
A10:  the carrier of GY is non empty by A6,XBOOLE_1:3;
A11: [#]GX = the carrier of GX by PRE_TOPC:12
.= F"the carrier of GY by A10,FUNCT_2:48
.= F" [#] GY by PRE_TOPC:12
.= F" A \/ F" B by A5,RELAT_1:175;
F" A /\ F" B = F"(A /\ B) by FUNCT_1:137
.= {} by A9,RELAT_1:171;
then A12:F" A misses F" B by XBOOLE_0:def 7;
A13: F" A is closed & F" B is closed by A1,A7,PRE_TOPC:def 12;
rng F = F.:(the carrier of GX) by A10,FUNCT_2:45;
then F"A <> {}GX & F"B <> {}GX by A4,A6,RELAT_1:174;
end;

::
::                          Connected Sets
::

definition let GX be TopStruct, A be Subset of GX;
attr A is connected means
:Def3: GX|A is connected;
end;

theorem Th16:
A is connected
iff for P,Q being Subset of GX st A = P \/ Q &
P,Q are_separated holds P = {}GX or Q = {}GX
proof A1:  [#](GX|A) = A & {}(GX|A) = {} by PRE_TOPC:def 10;
A2:   now given P,Q being Subset of GX such that
A3:  A = P \/ Q and
A4:  P,Q are_separated and
A5:  P <> {}GX & Q <> {}GX;
A6:  P c= [#](GX|A) & Q c= [#](GX|A) by A1,A3,XBOOLE_1:7;
then reconsider P1 = P as Subset of GX|A by PRE_TOPC:
16;
reconsider Q1 = Q as Subset of GX|A by A6,PRE_TOPC:16;
P1,Q1 are_separated by A1,A3,A4,Th7;
then not GX|A is connected by A1,A3,A5,Def2;
hence not A is connected by Def3;
end;
now assume not A is connected;
then not GX|A is connected by Def3;
then consider P,Q being Subset of GX|A such that
A7:  [#](GX|A) = P \/ Q and
A8:  P,Q are_separated and
A9:  P <> {}(GX|A) & Q <> {}(GX|A) by Def2;
reconsider P1 = P as Subset of GX by PRE_TOPC:39;
reconsider Q1 = Q as Subset of GX by PRE_TOPC:39;
P1,Q1 are_separated by A8,Th6;
hence ex P1,Q1 being Subset of GX st A = P1 \/ Q1 &
P1,Q1 are_separated & P1 <> {}GX & Q1 <> {}GX by A1,A7,A9;
end;
hence thesis by A2;
end;

theorem Th17:
A is connected & A c= B \/ C & B,C are_separated implies
A c= B or A c= C
proof assume that
A1:  A is connected and
A2:  A c= B \/ C and
A3:  B,C are_separated;
assume not A c= B & not A c= C;
then A meets B & A meets C by A2,XBOOLE_1:73;
then A4:  A /\ B <> {} & A /\ C <> {} by XBOOLE_0:def 7;
then A5:  A <> {}GX;
A /\ B c= B & A /\ C c= C by XBOOLE_1:17;
then A6:  A /\ B,A /\ C are_separated by A3,Th8;
(A /\ B) \/ (A /\ C) = A /\ (B \/ C) by XBOOLE_1:23
.= A by A2,XBOOLE_1:28;
end;

theorem Th18:
A is connected & B is connected & not A,B are_separated
implies A \/ B is connected
proof assume that
A1:  A is connected and
A2:  B is connected and
A3:  not A,B are_separated;
assume not A \/ B is connected;
then consider P,Q being Subset of GX such that
A4:  A \/ B = P \/ Q and
A5:  P,Q are_separated and
A6:  P <> {}GX and
A7:  Q <> {}GX by Th16;
P misses Q by A5,Th2;
then A8:  P /\ Q = {} by XBOOLE_0:def 7;
A9:     A c= P \/ Q & B c= P \/ Q by A4,XBOOLE_1:7;
A10:  now assume A c= P & B c= P;
then A \/ B c= P & P c= P \/ Q by XBOOLE_1:7,8;
then P \/ Q = P by A4,XBOOLE_0:def 10;
then Q c= P by XBOOLE_1:7;
end;
A11: not(A c= P & B c= Q) by A3,A5,Th8;
A12: not(A c= Q & B c= P) by A3,A5,Th8;
now assume A c= Q & B c= Q;
then A \/ B c= Q & Q c= Q \/ P by XBOOLE_1:7,8;
then Q \/ P = Q by A4,XBOOLE_0:def 10;
then P c= Q by XBOOLE_1:7;
end;
end;

theorem Th19:
C is connected & C c= A & A c= Cl C implies A is connected
proof assume that
A1:  C is connected and
A2:  C c= A and
A3:  A c= Cl C;
assume not A is connected;
then consider P,Q being Subset of GX such that
A4:  A = P \/ Q and
A5:  P,Q are_separated and
A6:  P <> {}GX & Q <> {}GX by Th16;
(Cl P) misses Q & P misses Cl Q by A5,Def1;
then A7: (Cl P) /\ Q = {} & P /\ Cl Q = {} by XBOOLE_0:def 7;
A8:   now assume C c= P;
then Cl C c= Cl P by PRE_TOPC:49;
then (Cl C) /\ Q c= (Cl P) /\ Q by XBOOLE_1:27;
then A9: (Cl C) /\ Q = {} by A7,XBOOLE_1:3;
A /\ Q c= (Cl C) /\ Q by A3,XBOOLE_1:27;
then A /\ Q = {} by A9,XBOOLE_1:3;
end;
now assume C c= Q;
then Cl C c= Cl Q by PRE_TOPC:49;
then P /\ Cl C c= P /\ Cl Q by XBOOLE_1:27;
then A10: P /\ Cl C = {} by A7,XBOOLE_1:3;
P /\ A c= P /\ Cl C by A3,XBOOLE_1:27;
then P /\ A = {} by A10,XBOOLE_1:3;
end;
end;

theorem Th20:
A is connected implies Cl A is connected
proof assume
A1:  A is connected;
A c= Cl A & Cl A c= Cl A by PRE_TOPC:48;
hence Cl A is connected by A1,Th19;
end;

theorem Th21:
GX is connected & A is connected & [#]GX \ A = B \/ C &
B,C are_separated implies A \/ B is connected & A \/ C is connected
proof
A1:  now let A,B,C be Subset of GX such that
A2:  GX is connected and
A3:  A is connected and
A4:  [#]GX \ A = B \/ C and
A5:  B,C are_separated;
now let P,Q be Subset of GX such that
A6:  A \/ B = P \/ Q and
A7:  P,Q are_separated;
A8:  [#]GX = A \/ (B \/ C) by A4,PRE_TOPC:24
.= P \/ Q \/ C by A6,XBOOLE_1:4;
A9:               A c= P \/ Q by A6,XBOOLE_1:7;
A10:  now assume
A c= P;
then Q,A are_separated by A7,Th8;
then A11: Q misses A by Th2;
Q c= B \/ A by A6,XBOOLE_1:7;
then Q c= B by A11,XBOOLE_1:73;
then Q,C are_separated by A5,Th8;
then A12: Q,P \/ C are_separated by A7,Th9;
[#]GX = Q \/ (P \/ C) by A8,XBOOLE_1:4;
then Q = {}GX or P \/ C = {}GX by A2,A12,Def2;
hence P = {}GX or Q = {}GX by XBOOLE_1:15;
end;
now assume A c= Q;
then P,A are_separated by A7,Th8;
then A13: P misses A by Th2;
P c= B \/ A by A6,XBOOLE_1:7;
then P c= B by A13,XBOOLE_1:73;
then P,C are_separated by A5,Th8;
then A14: P,Q \/ C are_separated by A7,Th9;
[#]GX = P \/ (Q \/ C) by A8,XBOOLE_1:4;
then P = {}GX or Q \/ C = {}GX by A2,A14,Def2;
hence P = {}GX or Q = {}GX by XBOOLE_1:15;
end;
hence P = {}GX or Q = {}GX by A3,A7,A9,A10,Th17;
end;
hence A \/ B is connected by Th16;
end;
assume that
A15:  GX is connected and
A16:  A is connected and
A17:  [#]GX \ A = B \/ C and
A18:  B,C are_separated;
thus A \/ B is connected & A \/ C is connected by A1,A15,A16,A17,A18;
end;

theorem
[#]GX \ A = B \/ C & B,C are_separated & A is closed implies
A \/ B is closed & A \/ C is closed
proof
A1:  now let A,B,C be Subset of GX; assume that
A2:  [#]GX \ A = B \/ C and
A3:  B,C are_separated and
A4:  A is closed;
A5:  Cl A = A by A4,PRE_TOPC:52;
A6:  [#]GX = A \/ (B \/ C) by A2,PRE_TOPC:24;
A7:  B c= Cl B & C c= Cl C by PRE_TOPC:48;
(Cl B) misses C & B misses Cl C by A3,Def1;
then A8:  (Cl B) /\ C = {} & B /\ Cl C = {} by XBOOLE_0:def 7;
Cl(A \/ B) = (Cl A) \/ Cl B by PRE_TOPC:50
.= A \/ ((Cl B) /\ (A \/ (B \/ C))) by A5,A6,PRE_TOPC:15
.= (A \/ Cl B) /\ (A \/ (A \/ (B \/ C))) by XBOOLE_1:24
.= (A \/ Cl B) /\ ((A \/ A) \/ (B \/ C)) by XBOOLE_1:4
.= A \/ ((Cl B) /\ (B \/ C)) by XBOOLE_1:24
.= A \/ (((Cl B) /\ B) \/ ((Cl B) /\ C)) by XBOOLE_1:23
.= A \/ B by A7,A8,XBOOLE_1:28;
hence A \/ B is closed by PRE_TOPC:52;
end;
assume that
A9:  [#]GX \ A = B \/ C and
A10:  B,C are_separated and
A11:  A is closed;
thus A \/ B is closed & A \/ C is closed by A1,A9,A10,A11;
end;

theorem
C is connected & C meets A & C \ A <> {}GX implies C meets Fr A
proof
assume that
A1:  C is connected and
A2:  C meets A & C \ A <> {}GX;
A3:   C /\ A <> {} by A2,XBOOLE_0:def 7;
A4:  C \ A = C /\ A` by SUBSET_1:32;
A5:  C = C /\ [#]GX by PRE_TOPC:15
.= C /\ ( A \/ A`) by PRE_TOPC:18
.= (C /\ A) \/ (C \ A) by A4,XBOOLE_1:23;
C /\ A c= A by XBOOLE_1:17;
then A6:  Cl (C /\ A) c= Cl A by PRE_TOPC:49;
A7:  A` c= Cl(A`) by PRE_TOPC:48;
A8:  A c= Cl A by PRE_TOPC:48;
C \ A c= A` by A4,XBOOLE_1:17;
then A9:  Cl (C \ A) c= Cl(A`) by PRE_TOPC:49;
not C /\ A,C \ A are_separated by A1,A2,A3,A5,Th16;
then (Cl(C /\ A)) meets (C \ A) or (C /\ A) meets Cl(C \ A)
by Def1;
then (Cl(C /\ A)) /\ (C \ A) <> {} or (C /\ A) /\ Cl(C \ A) <> {}
by XBOOLE_0:def 7;
then A10: ((Cl(C /\ A)) /\ (C \ A)) \/ ((C /\ A) /\ Cl(C \ A)) <> {} by
XBOOLE_1:15;
A11: ((Cl(C /\ A)) /\ (C \ A)) \/ ((C /\ A) /\ Cl(C \ A)) =
(((Cl(C /\ A)) /\ C) /\ (A`)) \/ ((C /\ A) /\ Cl(C /\ (A`)))
by A4,XBOOLE_1:16
.= ((C /\ Cl(C /\ A)) /\ (A`)) \/ (C /\ (A /\ Cl(C /\ (A`)))) by XBOOLE_1:
16
.= (C /\ ((Cl(C /\ A)) /\ (A`))) \/ (C /\ (A /\ Cl(C /\ (A`))))
by XBOOLE_1:16
.= C /\ ((Cl(C /\ A) /\ (A`)) \/ (A /\ Cl(C /\ A`))) by XBOOLE_1:23;
A12: (Cl(C /\ A)) /\ (A`) c= (Cl A) /\ Cl(A`) by A6,A7,XBOOLE_1:27;
A /\ Cl(C /\ (A`)) c= (Cl A) /\ Cl(A`) by A4,A8,A9,XBOOLE_1:27;
then ((Cl(C /\ A)) /\ (A`)) \/ (A /\ Cl(C /\ (A`))) c=
(Cl A) /\ Cl(A`) & C c= C by A12,XBOOLE_1:8;
then C /\ (((Cl(C /\ A)) /\ (A`)) \/ (A /\ Cl(C /\ (A`)))) c=
C /\ ((Cl A) /\ Cl(A`)) by XBOOLE_1:27;
then ((Cl(C /\ A)) /\ (C \ A)) \/ ((C /\ A) /\ Cl(C \ A)) c= C /\ Fr A
by A11,TOPS_1:def 2;
hence C /\ Fr A <> {} by A10,XBOOLE_1:3;
end;

theorem Th24:
for X' being SubSpace of GX,
A being Subset of GX,
B being Subset of X' st A = B
holds A is connected iff B is connected
proof
let X' be SubSpace of GX, A be Subset of GX,
B be Subset of X'; assume
A1: A = B;
A2:  [#](GX|A) = A & [#](X'|B) = B by PRE_TOPC:def 10;
reconsider GX' = GX, X = X' as TopSpace;
reconsider A' = A as Subset of GX';
reconsider B' = B as Subset of X;
A3:  the carrier of (GX|A) = [#](GX|A) by PRE_TOPC:12
.= the carrier of X'|B by A1,A2,PRE_TOPC:12;
A4:  {}(GX|A) = {}(X'|B);
A5:   now assume not A is connected;
then not GX'|A' is connected by Def3;
then consider P,Q being Subset of GX|A such that
A6:  [#](GX|A) = P \/ Q and
A7:  P <> {}(GX|A) and
A8:  Q <> {}(GX|A) and
A9:  P is closed and
A10:  Q is closed and
A11:  P misses Q by Th11;
consider P1 being Subset of GX such that
A12: P1 is closed and
A13: P1 /\ ([#](GX|A)) = P by A9,PRE_TOPC:43;
consider Q1 being Subset of GX such that
A14: Q1 is closed and
A15: Q1 /\ ([#](GX|A)) = Q by A10,PRE_TOPC:43;
reconsider PP = P, QQ=Q as Subset of X'|B by A3;
P1 /\ [#]X' c= [#]X' by XBOOLE_1:17;
then reconsider P11 = P1 /\ ([#](X')) as Subset of X' by PRE_TOPC:16;
A16: P11 is closed by A12,PRE_TOPC:43;
P1 /\ ([#](X')) c= P1 & A c= A by XBOOLE_1:17;
then A17: P1 /\ [#](X') /\ A c= P by A2,A13,XBOOLE_1:27;
A18: P1 /\ A c= P1 by XBOOLE_1:17;
A19: P1 /\ A c= A by XBOOLE_1:17;
A20: B c= [#](X') by PRE_TOPC:14;
P c= P \/ Q by XBOOLE_1:7;
then P c= [#](X') by A1,A2,A6,A20,XBOOLE_1:1;
then P c= P1 /\ ([#](X')) by A2,A13,A18,XBOOLE_1:19;
then P c= P1 /\ [#](X') /\ A by A2,A13,A19,XBOOLE_1:19;
then P11 /\ [#](X'|B) = PP by A1,A2,A17,XBOOLE_0:def 10;
then A21:  PP is closed by A16,PRE_TOPC:43;
Q1 /\ ([#](X')) c= [#](X') by XBOOLE_1:17;
then reconsider Q11 = Q1 /\ ([#](X')) as Subset of X' by PRE_TOPC:16;
A22: Q11 is closed by A14,PRE_TOPC:43;
Q1 /\ ([#](X')) c= Q1 & A c= A by XBOOLE_1:17;
then A23: (Q1 /\ ([#](X'))) /\ A c= Q by A2,A15,XBOOLE_1:27;
A24: Q1 /\ A c= Q1 by XBOOLE_1:17;
A25: Q1 /\ A c= A by XBOOLE_1:17;
A26: B c= [#](X') by PRE_TOPC:14;
Q c= P \/ Q by XBOOLE_1:7;
then Q c= [#](X') by A1,A2,A6,A26,XBOOLE_1:1;
then Q c= Q1 /\ ([#](X')) by A2,A15,A24,XBOOLE_1:19;
then Q c= (Q1 /\ ([#](X'))) /\ A by A2,A15,A25,XBOOLE_1:19;
then (Q1 /\ ([#](X'))) /\ A = Q by A23,XBOOLE_0:def 10;
then QQ is closed by A1,A2,A22,PRE_TOPC:43;
then not X|B' is connected by A1,A2,A4,A6,A7,A8,A11,A21,Th11;
hence not B is connected by Def3;
end;
now assume not B is connected;
then not X'|B is connected by Def3;
then consider P,Q being Subset of X'|B such that
A27:  [#](X'|B) = P \/ Q and
A28:  P <> {}(X'|B) and
A29:  Q <> {}(X'|B) and
A30:  P is closed and
A31:  Q is closed and
A32:  P misses Q by Th11;
consider P1 being Subset of X' such that
A33: P1 is closed and
A34: P1 /\ ([#](X'|B)) = P by A30,PRE_TOPC:43;
consider Q1 being Subset of X' such that
A35: Q1 is closed and
A36: Q1 /\ ([#](X'|B)) = Q by A31,PRE_TOPC:43;
consider P2 being Subset of GX such that
A37: P2 is closed and
A38: P2 /\ ([#](X')) = P1 by A33,PRE_TOPC:43;
consider Q2 being Subset of GX such that
A39: Q2 is closed and
A40: Q2 /\ ([#](X')) = Q1 by A35,PRE_TOPC:43;
reconsider PP = P as Subset of GX|A by A3;
reconsider QQ = Q as Subset of GX|A by A3;
P2 /\ ([#](GX|A)) = P2 /\ (([#](X')) /\ B) by A1,A2,PRE_TOPC:15
.= PP by A2,A34,A38,XBOOLE_1:16;
then A41:  PP is closed by A37,PRE_TOPC:43;
Q2 /\ ([#](GX|A)) = Q2 /\ (([#](X')) /\ B) by A1,A2,PRE_TOPC:15
.= QQ by A2,A36,A40,XBOOLE_1:16;
then QQ is closed by A39,PRE_TOPC:43;
then not GX'|A' is connected by A1,A2,A4,A27,A28,A29,A32,A41,Th11;
hence not A is connected by Def3;
end;
hence thesis by A5;
end;

theorem
A is closed & B is closed & A \/ B is connected & A /\ B is connected
implies
A is connected & B is connected
proof assume that
A1:  A is closed and
A2:  B is closed;
assume that
A3:  A \/ B is connected and
A4:  A /\ B is connected;
A5:  GX|(A \/ B) is connected by A3,Def3;
A6:  A \/ B = [#](GX|(A \/ B)) by PRE_TOPC:def 10;
set AB = A \/ B;
A7:  A c= A \/ B & B c= A \/ B by XBOOLE_1:7;
then reconsider A1 = A as Subset of GX|AB by A6,PRE_TOPC:16;
reconsider B1 = B as Subset of GX|AB by A6,A7,PRE_TOPC:16;
A8: [#](GX|(A \/ B)) \ (A1 /\ B1) = (A1 \ B1) \/ (B1 \ A1) by A6,XBOOLE_1:55;
A9: (A1 /\ B1) \/ (A1 \ B1) = A1 by XBOOLE_1:51;
A10: (A1 /\ B1) \/ (B1 \ A1) = B1 by XBOOLE_1:51;
A11: A /\ ([#](GX|(A \/ B))) = A by A6,A7,XBOOLE_1:28;
B /\ ([#](GX|(A \/ B))) = B by A6,A7,XBOOLE_1:28;
then A1 is closed & B1 is closed by A1,A2,A11,PRE_TOPC:43;
then A12: A1 \ B1,B1 \ A1 are_separated by Th10;
A1 /\ B1 is connected by A4,Th24;
then A1 is connected & B1 is connected by A5,A8,A9,A10,A12,Th21;
hence A is connected & B is connected by Th24;
end;

theorem Th26:
for F being Subset-Family of GX st
(for A being Subset of GX st A in F holds A is connected)
& (ex A being Subset of GX st A <> {}GX & A in F &
(for B being Subset of GX st B in F & B <> A holds
not A,B are_separated)) holds union F is connected
proof
let F be Subset-Family of GX;assume that
A1:  for A being Subset of GX st A in F holds A is connected and
A2:  ex A being Subset of GX st A <> {}GX & A in F &
(for B being Subset of GX st B in F & B <> A holds
not A,B are_separated);
consider A1 being Subset of GX such that
A3:  A1 <> {}GX & A1 in F and
A4:  for B being Subset of GX st B in F & B <> A1 holds
not A1,B are_separated by A2;
reconsider A1 as Subset of GX;
now
let P,Q be Subset of GX; assume that
A5:  union F = P \/ Q and
A6:  P,Q are_separated;
P misses Q by A6,Th2;
then A7:  P /\ Q = {} by XBOOLE_0:def 7;
A8:  A1 is connected by A1,A3;
A9:          A1 c= P \/ Q by A3,A5,ZFMISC_1:92;
A10:  now assume
A11:  A1 c= P;
A12:                now let B be Subset of GX; assume that
A13: B in F and
A14: B <> A1;assume
A15: not B c= P;
A16: not A1,B are_separated by A4,A13,A14;
A17: B is connected by A1,A13;
B c= P \/ Q by A5,A13,ZFMISC_1:92;
then B c= P or B c= Q by A6,A17,Th17;
end;
for A being set st A in F holds A c= P by A11,A12;
then A18:   union F c= P by ZFMISC_1:94;
P c= P \/ Q by XBOOLE_1:7;
then P = P \/ Q by A5,A18,XBOOLE_0:def 10;
then Q c= P by XBOOLE_1:7;
hence Q = {}GX by A7,XBOOLE_1:28;
end;
now assume
A19: A1 c= Q;
A20:               now let B be Subset of GX; assume that
A21: B in F and
A22: B <> A1 and
A23: not B c= Q;
A24: not A1,B are_separated by A4,A21,A22;
A25: B is connected by A1,A21;
B c= P \/ Q by A5,A21,ZFMISC_1:92;
then B c= P or B c= Q by A6,A25,Th17;
end;
for A being set st A in F holds A c= Q by A19,A20;
then A26:  union F c= Q by ZFMISC_1:94;
Q c= P \/ Q by XBOOLE_1:7;
then Q = P \/ Q by A5,A26,XBOOLE_0:def 10;
then P c= Q by XBOOLE_1:7;
hence P = {}GX by A7,XBOOLE_1:28;
end;
hence P = {}GX or Q = {}GX by A6,A8,A9,A10,Th17;
end;
hence union F is connected by Th16;
end;

theorem Th27:
for F being Subset-Family of GX st
(for A being Subset of GX st A in F holds A is connected)
& meet F <> {}GX holds union F is connected
proof
let F be Subset-Family of GX;assume that
A1:  for A being Subset of GX st A in F
holds A is connected and
A2:  meet F <> {}GX;
consider x being Point of GX such that
A3:  x in meet F by A2,PRE_TOPC:41;
meet F c= union F by SETFAM_1:3;
then consider A2 being set such that
A4:  x in A2 and
A5:  A2 in F by A3,TARSKI:def 4;
reconsider A2 as Subset of GX by A5;
A6:  A2 <> {}GX by A4;
now let B be Subset of GX such that
A7:    B in F and
B <> A2;
A2 c= Cl A2 & B c= Cl B by PRE_TOPC:48;
then (x in Cl A2 & x in B) or (x in A2 & x in Cl B)
by A3,A4,A7,SETFAM_1:def 1;
then Cl A2 /\ B <> {} or A2 /\ Cl B <> {} by XBOOLE_0:def 3;
then Cl A2 meets B or A2 meets Cl B by XBOOLE_0:def 7;
hence not A2,B are_separated by Def1;
end;
hence union F is connected by A1,A5,A6,Th26;
end;

theorem Th28:
:: do poprawienia, przy poprawnej definicji "connected" !!!
[#]GX is connected iff GX is connected
proof
A1:  {}(GX|[#]GX) = {}GX;
A2:  [#]GX = [#](GX|[#]GX) by PRE_TOPC:def 10;
A3:   now assume [#]GX is connected;
then A4: GX|[#]GX is connected by Def3;
now let P1,Q1 be Subset of GX such that
A5:  [#]GX = P1 \/ Q1 and
A6:  P1,Q1 are_separated;
A7:  P1 c= [#]GX & Q1 c= [#]GX by PRE_TOPC:14;
then reconsider P = P1 as Subset of (GX|([#]GX))
by A2,PRE_TOPC:16;
reconsider Q = Q1 as Subset of GX|([#]GX)
by A2,A7,PRE_TOPC:16;
P,Q are_separated by A2,A5,A6,Th7;
hence P1 = {}GX or Q1 = {}GX by A1,A2,A4,A5,Def2;
end;
hence GX is connected by Def2;
end;
now assume A8: GX is connected;
now let P1,Q1 be Subset of GX|([#]GX) such that
A9: [#](GX|[#]GX) = P1 \/ Q1 and
A10: P1,Q1 are_separated;
reconsider P = P1 as Subset of GX by PRE_TOPC:39;
reconsider Q = Q1 as Subset of GX by PRE_TOPC:39;
P,Q are_separated by A10,Th6;
hence P1 = {}(GX|([#]GX)) or Q1 = {}(GX|([#]GX))
by A1,A2,A8,A9,Def2;
end;
then GX|([#]GX) is connected by Def2;
hence [#]GX is connected by Def3;
end;
hence thesis by A3;
end;

theorem Th29:
for GX being non empty TopSpace
for x being Point of GX holds {x} is connected
proof
let GX be non empty TopSpace;
let x be Point of GX; assume
not {x} is connected;
then consider P,Q being Subset of GX such that
A1:  {x} = P \/ Q and
A2:  P,Q are_separated and
A3:  P <> {}GX and
A4:  Q <> {}GX by Th16;
P <> Q
proof assume not thesis;
then A5:   P /\ Q = P;
P misses Q by A2,Th2;
end;
end;

definition let GX be TopStruct, x,y be Point of GX;
pred x, y are_joined means
:Def4:ex C being Subset of GX st C is connected & x in C & y in C;
end;

theorem Th30:
for GX being non empty TopSpace st
ex x being Point of GX st for y being Point of GX holds x,y are_joined
holds GX is connected
proof
let GX be non empty TopSpace;
given a being Point of GX such that
A1: for x being Point of GX holds a,x are_joined;
A2: now let x be Point of GX;
a,x are_joined by A1;
hence ex C being Subset of GX st C is connected & a in C & x in C by Def4
;
end;
now let x be Point of GX;
defpred P[set] means
ex C1 being Subset of GX st C1 = \$1 & C1 is connected & x in \$1;
consider F being Subset-Family of GX such that
A3:     for C being Subset of GX holds C in F iff P[C]
from SubFamExS;
take F;
let C be Subset of GX;
thus C in F implies C is connected & x in C
proof
assume C in F;
then ex C1 being Subset of GX st C1 = C & C1 is connected & x in C by A3
;
hence thesis;
end;
thus C is connected & x in C implies C in F by A3;
end;
then consider F being Subset-Family of GX such that
A4:  for C being Subset of GX
holds C in F iff C is connected & a in C;
A5: for A being Subset of GX st A in F holds A is connected by A4;
A6: union F c= [#]GX by PRE_TOPC:14;
now let x be set; assume
x in [#]GX; then consider C being Subset of GX such that
A7:   C is connected and A8:a in C and A9:x in C by A2;
C in F by A4,A7,A8;
hence x in union F by A9,TARSKI:def 4;
end;
then [#]GX c= union F by TARSKI:def 3;
then A10: union F = [#]GX by A6,XBOOLE_0:def 10;
A11:  for A being set st A in F holds a in A by A4;
{a} is connected & a in {a} by Th29,TARSKI:def 1;
then F <> {} by A4;
then meet F <> {}GX by A11,SETFAM_1:def 1;
then [#]GX is connected by A5,A10,Th27;
hence GX is connected by Th28;
end;

theorem Th31:
(ex x being Point of GX st for y being Point of GX holds
x,y are_joined)
iff (for x,y being Point of GX holds x,y are_joined)
proof
A1:  now given a being Point of GX such that
A2:   for x being Point of GX holds a,x are_joined;
let x,y be Point of GX;
a,x are_joined by A2;
then consider C1 being Subset of GX such that
A3:   C1 is connected and
A4:   a in C1 and
A5:   x in C1 by Def4;
a,y are_joined by A2;
then consider C2 being Subset of GX such that
A6:   C2 is connected and
A7:   a in C2 and
A8:   y in C2 by Def4;
C1 /\ C2 <> {}GX by A4,A7,XBOOLE_0:def 3;
then C1 meets C2 by XBOOLE_0:def 7;
then not C1,C2 are_separated by Th2;
then A9:   C1 \/ C2 is connected by A3,A6,Th18;
x in C1 \/ C2 & y in C1 \/ C2 by A5,A8,XBOOLE_0:def 2;
hence x,y are_joined by A9,Def4;
end;
now assume
A10:   for x,y being Point of GX holds x,y are_joined;
consider a being Point of GX;
for y being Point of GX holds a,y are_joined by A10;
hence ex x being Point of GX st for y being Point of GX
holds x,y are_joined;
end;
hence thesis by A1;
end;

theorem
for GX being non empty TopSpace st
for x, y being Point of GX holds x,y are_joined holds
GX is connected
proof
let GX be non empty TopSpace;
assume for x,y being Point of GX holds x,y are_joined;
then ex x being Point of GX st
for y being Point of GX holds x,y are_joined by Th31;
hence GX is connected by Th30;
end;

theorem Th33:
for GX being non empty TopSpace
for x being Point of GX, F being Subset-Family of GX
st for A being Subset of GX holds A in F iff A is connected & x in A
holds F <> {}
proof
let GX be non empty TopSpace;
let x be Point of GX, F be Subset-Family of GX such that
A1: for A being Subset of GX holds A in F iff A is connected
& x in A;
{x} is connected & x in {x} by Th29,TARSKI:def 1;
hence F <> {} by A1;
end;

::
::              Components of Topological Spaces
::

definition let GX be TopStruct, A be Subset of GX;
pred A is_a_component_of GX means
:Def5:A is connected & for B being Subset of GX st
B is connected holds A c= B implies A = B;
end;

theorem Th34:
for GX being non empty TopSpace, A being Subset of GX
st A is_a_component_of GX holds A <> {}GX
proof let GX be non empty TopSpace, A be Subset of GX;
assume
A1: A is_a_component_of GX;
assume A2: not thesis;
consider x being Point of GX;
A3: {x} is connected by Th29;
{} c= {x} by XBOOLE_1:2;
end;

theorem
A is_a_component_of GX implies A is closed
proof
assume
A1: A is_a_component_of GX;
A2: A c= Cl A by PRE_TOPC:48;
A is connected by A1,Def5;
then Cl A is connected by Th20;
then A = Cl A by A1,A2,Def5;
hence A is closed by PRE_TOPC:52;
end;

theorem Th36:
A is_a_component_of GX & B is_a_component_of GX implies
A = B or A,B are_separated
proof assume
A1: A is_a_component_of GX & B is_a_component_of GX;
A <> B implies A,B are_separated
proof assume that
A2: A <> B and
A3:   not A,B are_separated;
A is connected & B is connected by A1,Def5;
then A4:   A \/ B is connected by A3,Th18;
A c= A \/ B & B c= A \/ B by XBOOLE_1:7;
then A = A \/ B & B = A \/ B by A1,A4,Def5;
end;
hence thesis;
end;

theorem Th37:
A is_a_component_of GX & B is_a_component_of GX implies
A = B or A misses B
proof assume that
A1: A is_a_component_of GX and
A2: B is_a_component_of GX;
A <> B implies A,B are_separated by A1,A2,Th36;
hence thesis by Th2;
end;

theorem
C is connected implies
for S being Subset of GX st S is_a_component_of GX holds
C misses S or C c= S
proof
assume
A1: C is connected;
let S be Subset of GX; assume
A2: S is_a_component_of GX;
assume C meets S;
then A3: not C,S are_separated by Th2;
S is connected by A2,Def5;
then A4: C \/ S is connected by A1,A3,Th18;
S c= C \/ S by XBOOLE_1:7;
then S = C \/ S by A2,A4,Def5;
hence C c= S by XBOOLE_1:7;
end;

definition let GX be TopStruct, A, B be Subset of GX;
pred B is_a_component_of A means
:Def6:ex B1 being Subset of GX|A st B1 = B & B1 is_a_component_of GX|A;
end;

theorem
GX is connected & A is connected & C is_a_component_of [#]GX \ A implies
[#]GX \ C is connected
proof assume that
A1:  GX is connected and
A2:  A is connected and
A3:  C is_a_component_of [#]GX \ A;
consider C1 being Subset of GX|([#]GX \ A) such that
A4:  C1 = C and
A5:  C1 is_a_component_of GX|([#]GX \ A) by A3,Def6;
A6:  C1 is connected by A5,Def5;
reconsider C2 = C1 as Subset of GX by A4;
C1 c= [#](GX|([#]GX \ A)) by PRE_TOPC:14;
then C1 c= [#]GX \ A by PRE_TOPC:def 10;
then ([#]GX \ A)` c= C2` by PRE_TOPC:19;
then [#]GX \ ([#]GX \ A) c= C2` by PRE_TOPC:17;
then A7:  A c= C2` by PRE_TOPC:22;
then A8: A c= [#]GX \ C2 by PRE_TOPC:17;
now let P,Q be Subset of GX such that
A9:  [#]GX \ C = P \/ Q and
A10:  P,Q are_separated;
A11:  P misses Q by A10,Th2;
A12: Q c= [#]GX \ C by A9,XBOOLE_1:7;
A misses C1 by A7,PRE_TOPC:21;
then A13:   A /\ C1 = {} by XBOOLE_0:def 7;
A14: C is connected by A4,A6,Th24;
A15:   P misses P` by PRE_TOPC:26;
A16:  now assume
A17: A c= P;
Q c= P` by A11,PRE_TOPC:21;
then A /\ Q c= P /\ P` by A17,XBOOLE_1:27;
then A18: A /\ Q c= {} by A15,XBOOLE_0:def 7;
(C \/ Q) /\ A = (A /\ C) \/ (A /\ Q) by XBOOLE_1:23
.= {} by A4,A13,A18,XBOOLE_1:3;
then (C \/ Q) misses A by XBOOLE_0:def 7;
then C \/ Q c= A` by PRE_TOPC:21;
then C \/ Q c= [#]GX \ A by PRE_TOPC:17;
then C \/ Q c= [#](GX|([#]GX \ A)) by PRE_TOPC:def 10;
then reconsider C1Q1 = C \/ Q as
Subset of GX|([#]GX \ A) by PRE_TOPC:16;
C \/ Q is connected by A1,A9,A10,A14,Th21;
then A19: C1Q1 is connected by Th24;
A20:             C misses C` by PRE_TOPC:26;
C1 c= C1 \/ Q by XBOOLE_1:7;
then C1Q1 = C1 by A4,A5,A19,Def5;
then Q c= C by A4,XBOOLE_1:7;
then Q c= C /\ ([#]GX \ C) by A12,XBOOLE_1:19;
then Q c= C /\ C` by PRE_TOPC:17;
then Q c= {} by A20,XBOOLE_0:def 7;
hence Q = {}GX by XBOOLE_1:3;
end;
now assume
A21: A c= Q;
A22:             Q misses Q` by PRE_TOPC:26;
P c= Q` by A11,PRE_TOPC:21;
then A /\ P c= Q /\ Q` by A21,XBOOLE_1:27;
then A23: A /\ P c= {} by A22,XBOOLE_0:def 7;
(C \/ P ) /\ A = (A /\ C) \/ (A /\ P) by XBOOLE_1:23
.= {} by A4,A13,A23,XBOOLE_1:3;
then C \/ P misses A by XBOOLE_0:def 7;
then C \/ P c= A` by PRE_TOPC:21;
then C \/ P c= [#]GX \ A by PRE_TOPC:17;
then C \/ P c= [#](GX|([#]GX \ A)) by PRE_TOPC:def 10;
then reconsider C1P1 = C \/ P as
Subset of GX|([#]GX \ A) by PRE_TOPC:16;
C \/ P is connected by A1,A9,A10,A14,Th21;
then A24: C1P1 is connected by Th24;
C c= C1 \/ P by A4,XBOOLE_1:7;
then C1P1 = C1 by A4,A5,A24,Def5;
then A25: P c= C by A4,XBOOLE_1:7;
A26:             C misses C` by PRE_TOPC:26;
P c= [#]GX \ C by A9,XBOOLE_1:7;
then P c= C /\ ([#]GX \ C) by A25,XBOOLE_1:19;
then P c= C /\ C` by PRE_TOPC:17;
then P c= {} by A26,XBOOLE_0:def 7;
hence P = {}GX by XBOOLE_1:3;
end;
hence P = {}GX or Q = {}GX by A2,A4,A8,A9,A10,A16,Th17;
end;
hence [#]GX \ C is connected by Th16;
end;

::
::                    A Component of a Point
::

definition let GX be TopStruct, x be Point of GX;
func skl x -> Subset of GX means
:Def7:ex F being Subset-Family of GX st
(for A being Subset of GX holds A in F iff A is connected & x in A) &
union F = it;
existence
proof
defpred P[set] means
ex A1 being Subset of GX st A1 = \$1 & A1 is connected & x in \$1;
consider F being Subset-Family of GX such that
A1:  for A being Subset of GX holds A in F iff P[A]
from SubFamExS;
take S = union F, F;
thus for A being Subset of GX holds A in F iff A is connected & x in A
proof
let A be Subset of GX;
thus A in F implies A is connected & x in A
proof
assume A in F;
then ex A1 being Subset of GX st A1 = A & A1 is connected & x in A by
A1;
hence thesis;
end;
thus thesis by A1;
end;
thus union F = S;
end;
uniqueness
proof let S,S' be Subset of GX; assume
A2:  (ex F being Subset-Family of GX st
(for A being Subset of GX holds A in F iff A is connected &
x in A) & union F = S) & ex F' being Subset-Family of GX st
(for A being Subset of GX holds A in F' iff A is connected &
x in A) & union F' = S';
then consider F being Subset-Family of GX such that
A3:  (for A being Subset of GX holds A in F iff A is connected
& x in A) & union F = S;
consider F' being Subset-Family of GX such that
A4: (for A being Subset of GX holds A in F' iff A is connected
& x in A) & union F' = S' by A2;
now let y be set;
A5:  now assume
y in S;
then consider B being set such that
A6: y in B & B in F by A3,TARSKI:def 4;
reconsider B as Subset of GX by A6;
B is connected & x in B & y in B by A3,A6;
then B in F'& y in B by A4;
hence y in S' by A4,TARSKI:def 4;
end;
now assume
y in S';
then consider B being set such that
A7: y in B & B in F' by A4,TARSKI:def 4;
reconsider B as Subset of GX by A7;
B is connected & x in B & y in B by A4,A7;
then B in F & y in B by A3;
hence y in S by A3,TARSKI:def 4;
end;
hence y in S iff y in S' by A5;
end;
hence S = S' by TARSKI:2;
end;
end;

reserve GX for non empty TopSpace;
reserve A, C for Subset of GX;
reserve x for Point of GX;

theorem Th40:
x in skl x
proof
consider F being Subset-Family of GX such that
A1: for A being Subset of GX holds A in F iff A is connected & x in A and
A2: skl x = union F by Def7;
A3: F <> {} by A1,Th33;
for A being set holds A in F implies x in A by A1;
then A4: x in meet F by A3,SETFAM_1:def 1;
meet F c= union F by SETFAM_1:3;
hence x in skl x by A2,A4;
end;

theorem Th41:
skl x is connected
proof
consider F being Subset-Family of GX such that
A1: for A being Subset of GX holds A in F iff A is connected & x in A and
A2: skl x = union F by Def7;
A3: for A being set holds A in F implies x in A by A1;
A4: for A being Subset of GX st A in F holds A is connected by A1;
F <> {} by A1,Th33;
then meet F <> {}GX by A3,SETFAM_1:def 1;
hence skl x is connected by A2,A4,Th27;
end;

theorem Th42:
C is connected & skl x c= C implies C = skl x
proof assume
A1: C is connected; assume
A2: skl x c= C;
consider F being Subset-Family of GX such that
A3: for A being Subset of GX holds (A in F iff A is connected & x in A) and
A4: skl x = union F by Def7;
x in skl x by Th40;
then C in F by A1,A2,A3;
then C c= skl x by A4,ZFMISC_1:92;
hence C = skl x by A2,XBOOLE_0:def 10;
end;

theorem Th43:
A is_a_component_of GX iff ex x being Point of GX st A = skl x
proof
A1:  now assume
A2:   A is_a_component_of GX;
then A3:   A <> {}GX & A is connected by Def5,Th34;
then consider y being Point of GX such that
A4:   y in A by PRE_TOPC:41;
take x = y;
consider F being Subset-Family of GX such that
A5:   for B being Subset of GX holds B in F iff B is connected & x in B and
A6:   union F = skl x by Def7;
A in F by A3,A4,A5;
then A7:   A c= union F by ZFMISC_1:92;
skl x is connected by Th41;
hence A = skl x by A2,A6,A7,Def5;
end;
now given x being Point of GX such that
A8:   A = skl x;
A is connected &
for B being Subset of GX st B is connected
holds A c= B implies A = B by A8,Th41,Th42;
hence A is_a_component_of GX by Def5;
end;
hence thesis by A1;
end;

theorem
A is_a_component_of GX & x in A implies A = skl x
proof assume that
A1: A is_a_component_of GX and
A2: x in A; assume
A3: A <> skl x;
x in skl x by Th40;
then A /\ (skl x) <> {} by A2,XBOOLE_0:def 3;
then A4: A meets (skl x) by XBOOLE_0:def 7;
skl x is_a_component_of GX by Th43;
then A,skl x are_separated by A1,A3,Th36;
end;

theorem
A = skl x implies
for p being Point of GX st p in A holds skl p = A
proof assume
A1: A = skl x; given p being Point of GX such that
A2: p in A and
A3: skl p <> A;
skl p is_a_component_of GX & A is_a_component_of GX by A1,Th43;
then (skl p) misses A by A3,Th37;
then A4: (skl p) /\ A = {}GX by XBOOLE_0:def 7;
p in skl p by Th40;
end;

theorem
for F being Subset-Family of GX st for A being Subset of GX
holds A in F iff A is_a_component_of GX
holds F is_a_cover_of GX
proof let F  be Subset-Family of GX such that
A1: for A being Subset of GX holds A in F iff A is_a_component_of GX;
A2: union F c= [#]GX by PRE_TOPC:14;
now let x be set; assume
x in [#]GX;
then reconsider y = x as Point of GX;
skl y is_a_component_of GX by Th43;
then skl y in F by A1;
then A3:   skl y c= union F by ZFMISC_1:92;
y in skl y by Th40;
hence x in union F by A3;
end;
then [#]GX c= union F by TARSKI:def 3;
then union F = [#]GX by A2,XBOOLE_0:def 10;
hence F is_a_cover_of GX by PRE_TOPC:def 8;
end;
```