
theorem Th2:
  for G being non-Dmulti _Graph holds G.size() c= G.order() *` G.order()
proof
  let G be non-Dmulti _Graph;
  consider f being one-to-one Function such that
    A1: dom f = the_Edges_of G &
      rng f c= [: the_Vertices_of G, the_Vertices_of G :] and
    for e being object st e in dom f holds
      f.e = [(the_Source_of G).e,(the_Target_of G).e] by Th1;
  G.size() c= card [: the_Vertices_of G, the_Vertices_of G :]
    by A1, CARD_1:10;
  then G.size() c= card [: G.order(), card the_Vertices_of G :] by CARD_2:7;
  hence thesis by CARD_2:def 2;
end;
