
theorem
  for G1, G2 being _Graph, F being one-to-one PGraphMapping of G1, G2
  st F is isomorphism holds card(G1.loops()) = card(G2.loops())
proof
  let G1, G2 be _Graph, F be one-to-one PGraphMapping of G1, G2;
  assume F is isomorphism;
  then card G1.loops() c= card G2.loops() & card G2.loops() c= card G1.loops()
    by Th92, Th93;
  hence thesis by XBOOLE_0:def 10;
end;
