let F1, F2 be FUNCTION_DOMAIN of the carrier of G,the carrier of G; :: thesis: ( ( for f being Element of F1 holds f is Homomorphism of G,G ) & ( for h being Homomorphism of G,G holds
( h in F1 iff ( h is one-to-one & h is onto ) ) ) & ( for f being Element of F2 holds f is Homomorphism of G,G ) & ( for h being Homomorphism of G,G holds
( h in F2 iff ( h is one-to-one & h is onto ) ) ) implies F1 = F2 )
assume that
A6: ( ( for f being Element of F1 holds f is Homomorphism of G,G ) & ( for h being Homomorphism of G,G holds
( h in F1 iff ( h is one-to-one & h is onto ) ) ) ) and
A7: ( ( for f being Element of F2 holds f is Homomorphism of G,G ) & ( for h being Homomorphism of G,G holds
( h in F2 iff ( h is one-to-one & h is onto ) ) ) ) ; :: thesis: F1 = F2
A8: F1 c= F2

proof

let q be set ; :: according to TARSKI:def 3 :: thesis: ( not q in F1 or q in F2 )
assume A9: q in F1 ; :: thesis: q in F2
then reconsider h1 = q as Homomorphism of G,G by A6;
( h1 is one-to-one & h1 is onto ) by A6, A9;
hence q in F2 by A7; :: thesis: verum

end;

F2 c= F1

proof

let q be set ; :: according to TARSKI:def 3 :: thesis: ( not q in F2 or q in F1 )
assume A10: q in F2 ; :: thesis: q in F1
then reconsider h1 = q as Homomorphism of G,G by A7;
( h1 is one-to-one & h1 is onto ) by A7, A10;
hence q in F1 by A6; :: thesis: verum

end;

hence F1 = F2 by A8, XBOOLE_0:def 10; :: thesis: verum