for G3 being _Graph
for G4 being b₁ -isomorphic _Graph
for v1, v2 being object
for G1 being addVertex of G3,v1
for G2 being addVertex of G4,v2 holds
not ( ( v1 in the_Vertices_of G3 implies v2 in the_Vertices_of G4 ) & ( v2 in the_Vertices_of G4 implies v1 in the_Vertices_of G3 ) & not G2 is G1 -isomorphic )