let x1, x2 be set ; :: thesis:
let C be Category; :: thesis:
let c be Object of C; :: thesis:
let i1, i2 be Morphism of C; :: thesis:
set F = (x1,x2) --> (i1,i2);
set I = {x1,x2};
assume A1: x1 <> x2 ; :: thesis:
thus ( c is_a_coproduct_wrt i1,i2 implies c is_a_coproduct_wrt (x1,x2) --> (i1,i2) ) :: thesis:

assume A2: c is_a_coproduct_wrt i1,i2 ; :: thesis:
then ( cod i1 = c & cod i2 = c ) ;
hence (x1,x2) --> (i1,i2) is Injections_family of c,{x1,x2} by Th65; :: according to CAT_3:def 17 :: thesis:
let b be Object of C; :: thesis:
let F9 be Injections_family of b,{x1,x2}; :: thesis:
assume A3: doms ((x1,x2) --> (i1,i2)) = doms F9 ; :: thesis:
set f = F9 /. x1;
set g = F9 /. x2;
A4: x1 in {x1,x2} by TARSKI:def 2;
then (doms ((x1,x2) --> (i1,i2))) /. x1 = dom (((x1,x2) --> (i1,i2)) /. x1) by Def1;
then dom (F9 /. x1) = dom (((x1,x2) --> (i1,i2)) /. x1) by A3, A4, Def1;
then A5: dom (F9 /. x1) = dom i1 by A1, Th3;
A6: x2 in {x1,x2} by TARSKI:def 2;
then (doms ((x1,x2) --> (i1,i2))) /. x2 = dom (((x1,x2) --> (i1,i2)) /. x2) by Def1;
then dom (F9 /. x2) = dom (((x1,x2) --> (i1,i2)) /. x2) by A3, A6, Def1;
then A7: dom (F9 /. x2) = dom i2 by A1, Th3;
cod (F9 /. x2) = b by A6, Th62;
then A8: F9 /. x2 in Hom ((dom i2),b) by A7;
cod (F9 /. x1) = b by A4, Th62;
then F9 /. x1 in Hom ((dom i1),b) by A5;
then consider h being Morphism of C such that
A9: h in Hom (c,b) and
A10: for k being Morphism of C st k in Hom (c,b) holds
( ( k (*) i1 = F9 /. x1 & k (*) i2 = F9 /. x2 ) iff h = k ) by A2, A8;
take h ; :: thesis:
thus h in Hom (c,b) by A9; :: thesis:
let k be Morphism of C; :: thesis:
assume A11: k in Hom (c,b) ; :: thesis:
thus ( ( for x being set st x in {x1,x2} holds
k (*) (((x1,x2) --> (i1,i2)) /. x) = F9 /. x ) implies h = k ) :: thesis:

assume A12: for x being set st x in {x1,x2} holds
k (*) (((x1,x2) --> (i1,i2)) /. x) = F9 /. x ; :: thesis:
then k (*) (((x1,x2) --> (i1,i2)) /. x2) = F9 /. x2 by A6;
then A13: k (*) i2 = F9 /. x2 by A1, Th3;
k (*) (((x1,x2) --> (i1,i2)) /. x1) = F9 /. x1 by A4, A12;
then k (*) i1 = F9 /. x1 by A1, Th3;
hence h = k by A10, A11, A13; :: thesis:

end;

assume h = k ; :: thesis:
then A14: ( k (*) i1 = F9 /. x1 & k (*) i2 = F9 /. x2 ) by A10, A11;
let x be set ; :: thesis:
assume x in {x1,x2} ; :: thesis:
then ( x = x1 or x = x2 ) by TARSKI:def 2;
hence k (*) (((x1,x2) --> (i1,i2)) /. x) = F9 /. x by A1, A14, Th3; :: thesis:

end;

assume A15: c is_a_coproduct_wrt (x1,x2) --> (i1,i2) ; :: thesis:
then A16: (x1,x2) --> (i1,i2) is Injections_family of c,{x1,x2} ;
x2 in {x1,x2} by TARSKI:def 2;
then A17: cod (((x1,x2) --> (i1,i2)) /. x2) = c by A16, Th62;
x1 in {x1,x2} by TARSKI:def 2;
then cod (((x1,x2) --> (i1,i2)) /. x1) = c by A16, Th62;
hence ( cod i1 = c & cod i2 = c ) by A1, A17, Th3; :: according to CAT_3:def 18 :: thesis:
let d be Object of C; :: thesis:
let f, g be Morphism of C; :: thesis:
assume that
A18: f in Hom ((dom i1),d) and
A19: g in Hom ((dom i2),d) ; :: thesis:
( cod f = d & cod g = d ) by A18, A19, CAT_1:1;
then reconsider F9 = (x1,x2) --> (f,g) as Injections_family of d,{x1,x2} by Th65;
doms ((x1,x2) --> (i1,i2)) = (x1,x2) --> ((dom i1),(dom i2)) by Th6
.= (x1,x2) --> ((dom f),(dom i2)) by A18, CAT_1:1
.= (x1,x2) --> ((dom f),(dom g)) by A19, CAT_1:1
.= doms F9 by Th6 ;
then consider h being Morphism of C such that
A20: h in Hom (c,d) and
A21: for k being Morphism of C st k in Hom (c,d) holds
( ( for x being set st x in {x1,x2} holds
k (*) (((x1,x2) --> (i1,i2)) /. x) = F9 /. x ) iff h = k ) by A15;
take h ; :: thesis:
thus h in Hom (c,d) by A20; :: thesis:
let k be Morphism of C; :: thesis:
assume A22: k in Hom (c,d) ; :: thesis:
thus ( k (*) i1 = f & k (*) i2 = g implies h = k ) :: thesis:

assume A23: ( k (*) i1 = f & k (*) i2 = g ) ; :: thesis:

let x be set ; :: thesis:
assume x in {x1,x2} ; :: thesis:
then ( x = x1 or x = x2 ) by TARSKI:def 2;
then ( ( ((x1,x2) --> (i1,i2)) /. x = i1 & F9 /. x = f ) or ( ((x1,x2) --> (i1,i2)) /. x = i2 & F9 /. x = g ) ) by A1, Th3;
hence k (*) (((x1,x2) --> (i1,i2)) /. x) = F9 /. x by A23; :: thesis:

end;

end;

assume A24: h = k ; :: thesis:
x2 in {x1,x2} by TARSKI:def 2;
then k (*) (((x1,x2) --> (i1,i2)) /. x2) = F9 /. x2 by A21, A22, A24;
then A25: k (*) (((x1,x2) --> (i1,i2)) /. x2) = g by A1, Th3;
x1 in {x1,x2} by TARSKI:def 2;
then k (*) (((x1,x2) --> (i1,i2)) /. x1) = F9 /. x1 by A21, A22, A24;
then k (*) (((x1,x2) --> (i1,i2)) /. x1) = f by A1, Th3;
hence ( k (*) i1 = f & k (*) i2 = g ) by A1, A25, Th3; :: thesis: