let V be SetValuation; :: according to HILBERT3:def 7 :: thesis: ex x being set st
for P being Permutation of V holds x is_a_fixpoint_of Perm (P,((p '&' q) => q))
take f = pr2 ((SetVal (V,p)),(SetVal (V,q))); :: thesis: for P being Permutation of V holds f is_a_fixpoint_of Perm (P,((p '&' q) => q))
let P be Permutation of V; :: thesis: f is_a_fixpoint_of Perm (P,((p '&' q) => q))
A5: dom (Perm (P,((p '&' q) => q))) = SetVal (V,((p '&' q) => q)) by FUNCT_2:def 1
.= Funcs ((SetVal (V,(p '&' q))),(SetVal (V,q))) by Def2
.= Funcs ([:(SetVal (V,p)),(SetVal (V,q)):],(SetVal (V,q))) by Def2 ;
hence f in dom (Perm (P,((p '&' q) => q))) by FUNCT_2:8; :: according to ABIAN:def 3 :: thesis: f = (Perm (P,((p '&' q) => q))) . f
then f in Funcs ((SetVal (V,(p '&' q))),(SetVal (V,q))) by A5, Def2;
then reconsider F = f as Function of (SetVal (V,(p '&' q))),(SetVal (V,q)) by FUNCT_2:66;
thus (Perm (P,((p '&' q) => q))) . f = ((Perm (P,q)) * F) * ((Perm (P,(p '&' q))) ") by Th36
.= ((Perm (P,q)) * F) * ([:(Perm (P,p)),(Perm (P,q)):] ") by Th34
.= ((Perm (P,q)) * F) * [:((Perm (P,p)) "),((Perm (P,q)) "):] by FUNCTOR0:6
.= (Perm (P,q)) * (F * [:((Perm (P,p)) "),((Perm (P,q)) "):]) by RELAT_1:36
.= (Perm (P,q)) * (((Perm (P,q)) ") * F) by Th16
.= ((Perm (P,q)) * ((Perm (P,q)) ")) * F by RELAT_1:36
.= (id (SetVal (V,q))) * F by FUNCT_2:61
.= f by FUNCT_2:17 ; :: thesis: verum