consider C being strict preorder category such that
A1:
Ob C = 2
and
for o1, o2 being Object of C st o1 in o2 holds
Hom (o1,o2) = {[o1,o2]}
and
A2:
RelOb C = RelIncl 2
and
A3:
Mor C = 2 \/ { [o1,o2] where o1, o2 is Element of 2 : o1 in o2 }
by Th37;
A4:
C is 2 -ordered
by A2, WELLORD1:38;
then A5:
C ~= OrdC 2
by Th38;
consider F being Functor of C,(OrdC 2), G being Functor of (OrdC 2),C such that
A6:
( F is covariant & G is covariant )
and
A7:
( G (*) F = id C & F (*) G = id (OrdC 2) )
by A4, Th38, CAT_6:def 28;
( 0 in 1 & 0 is Element of 2 & 1 is Element of 2 )
by CARD_1:49, CARD_1:50, TARSKI:def 1, TARSKI:def 2;
then A8:
[0,1] in { [o1,o2] where o1, o2 is Element of 2 : o1 in o2 }
;
then A9:
[0,1] in Mor C
by A3, XBOOLE_0:def 3;
reconsider g = [0,1] as morphism of C by A8, A3, XBOOLE_0:def 3;
A10:
not C is empty
by A1;
A11:
not g is identity
set f = F . g;
take
F . g
; ( not F . g is identity & Ob (OrdC 2) = {(dom (F . g)),(cod (F . g))} & Mor (OrdC 2) = {(dom (F . g)),(cod (F . g)),(F . g)} & dom (F . g), cod (F . g),F . g are_mutually_distinct )
thus A12:
not F . g is identity
( Ob (OrdC 2) = {(dom (F . g)),(cod (F . g))} & Mor (OrdC 2) = {(dom (F . g)),(cod (F . g)),(F . g)} & dom (F . g), cod (F . g),F . g are_mutually_distinct )proof
assume A13:
F . g is
identity
;
contradiction
[0,1] in the
carrier of
C
by A9, CAT_6:def 1;
then
(id the carrier of C) . [0,1] = [0,1]
by FUNCT_1:18;
then A14:
(id C) . [0,1] = g
by STRUCT_0:def 4;
G . (F . g) is
identity
by A13, CAT_6:def 22, A6, CAT_6:def 25;
then
(G (*) F) . g is
identity
by A6, A10, CAT_6:34;
hence
contradiction
by A11, A7, A10, A14, CAT_6:def 21;
verum
end;
card (Ob (OrdC 2)) = card 2
by A1, A5, Th14;
then consider x, y being object such that
A15:
( x <> y & Ob (OrdC 2) = {x,y} )
by CARD_2:60;
A16:
( dom (F . g) = x or dom (F . g) = y )
by A15, TARSKI:def 2;
A17:
dom (F . g) <> cod (F . g)
hence A19:
Ob (OrdC 2) = {(dom (F . g)),(cod (F . g))}
by A15, A16, TARSKI:def 2; ( Mor (OrdC 2) = {(dom (F . g)),(cod (F . g)),(F . g)} & dom (F . g), cod (F . g),F . g are_mutually_distinct )
for x being object holds
( x in Mor (OrdC 2) iff x in {(dom (F . g)),(cod (F . g)),(F . g)} )
proof
let x be
object ;
( x in Mor (OrdC 2) iff x in {(dom (F . g)),(cod (F . g)),(F . g)} )
hereby ( x in {(dom (F . g)),(cod (F . g)),(F . g)} implies x in Mor (OrdC 2) )
assume A20:
x in Mor (OrdC 2)
;
x in {(dom (F . g)),(cod (F . g)),(F . g)}then A21:
x in the
carrier of
(OrdC 2)
by CAT_6:def 1;
reconsider f1 =
x as
morphism of
(OrdC 2) by A20;
per cases
( f1 is identity or not f1 is identity )
;
suppose A22:
not
f1 is
identity
;
x in {(dom (F . g)),(cod (F . g)),(F . g)}A23:
(id the carrier of (OrdC 2)) . x = x
by A21, FUNCT_1:18;
A24:
F . (G . f1) =
(F (*) G) . f1
by A6, CAT_6:34
.=
(id the carrier of (OrdC 2)) . f1
by A7, STRUCT_0:def 4
.=
f1
by A23, CAT_6:def 21
;
not
G . f1 is
identity
by A24, A22, CAT_6:def 22, A6, CAT_6:def 25;
then
not
G . f1 in 2
by A1, A10, CAT_6:22;
then
G . f1 in { [o1,o2] where o1, o2 is Element of 2 : o1 in o2 }
by A3, XBOOLE_0:def 3;
then consider o1,
o2 being
Element of 2
such that A25:
(
G . f1 = [o1,o2] &
o1 in o2 )
;
A26:
(
o1 = 0 or
o1 = 1 )
by CARD_1:50, TARSKI:def 2;
(
o2 = 0 or
o2 = 1 )
by CARD_1:50, TARSKI:def 2;
hence
x in {(dom (F . g)),(cod (F . g)),(F . g)}
by A25, A26, A24, ENUMSET1:def 1, CARD_1:49, TARSKI:def 1;
verum end; end;
end;
assume
x in {(dom (F . g)),(cod (F . g)),(F . g)}
;
x in Mor (OrdC 2)
then A27:
x in {(dom (F . g)),(cod (F . g))} \/ {(F . g)}
by ENUMSET1:3;
end;
hence
Mor (OrdC 2) = {(dom (F . g)),(cod (F . g)),(F . g)}
by TARSKI:2; dom (F . g), cod (F . g),F . g are_mutually_distinct
( dom (F . g) <> cod (F . g) & dom (F . g) <> F . g & cod (F . g) <> F . g )
by A12, A17, CAT_6:22;
hence
dom (F . g), cod (F . g),F . g are_mutually_distinct
by ZFMISC_1:def 5; verum