let G1 be _Graph; :: thesis: for G2, G3 being DSimpleGraph of G1 holds G3 is G2 -Disomorphic
let G2, G3 be DSimpleGraph of G1; :: thesis: G3 is G2 -Disomorphic
G1 is G1 -Disomorphic by Th53;
hence G3 is G2 -Disomorphic by Th174; :: thesis: verum