let G1 be _Graph; :: thesis: for G2, G3 being GraphComplement of G1 holds G3 is G2 -isomorphic
let G2, G3 be GraphComplement of G1; :: thesis: G3 is G2 -isomorphic
G1 is G1 -isomorphic by GLIB_010:53;
hence G3 is G2 -isomorphic by Th103; :: thesis: verum