let G, H be Group; :: thesis: for a being Element of G
for g being Homomorphism of G,H holds g . (a ") = (g . a) "
let a be Element of G; :: thesis: for g being Homomorphism of G,H holds g . (a ") = (g . a) "
let g be Homomorphism of G,H; :: thesis: g . (a ") = (g . a) "
(g . (a ")) * (g . a) = g . ((a ") * a) by Def6
.= g . (1_ G) by GROUP_1:def 5
.= 1_ H by Th31 ;
hence g . (a ") = (g . a) " by GROUP_1:12; :: thesis: verum