
theorem Th70:
  for G1, G2 being _Graph, F being one-to-one PGraphMapping of G1, G2
  holds (F")" = F
proof
  let G1, G2 be _Graph, F be one-to-one PGraphMapping of G1, G2;
  thus (F")" = [F_V, (F_E")"] by FUNCT_1:43
    .= [F_V, F_E] by FUNCT_1:43
    .= F;
end;
