
theorem Th49:
  for G being _Graph holds G is edgeless iff G.size() = 0
proof
  let G be _Graph;
  hereby
    assume G is edgeless;
    then card the_Edges_of G = 0;
    hence G.size() = 0 by GLIB_000:def 25;
  end;
  assume G.size() = 0;
  then card the_Edges_of G = 0 by GLIB_000:def 25;
  hence thesis;
end;
