
theorem Th85:
  for G1, G2, G3, G4 being _Graph, F1 being empty PGraphMapping of G1, G2
  for F2 being empty PGraphMapping of G3, G4 holds F1 = F2
proof
  let G1, G2, G3, G4 be _Graph, F1 be empty PGraphMapping of G1, G2;
  let F2 be empty PGraphMapping of G3, G4;
  [F1_V, F1_E] = [F2_V, F2_E];
  hence thesis;
end;
