
theorem Th4:
  for G1, G2 being _Graph st G1 == G2
  holds G1 is loopfull implies G2 is loopfull
proof
  let G1, G2 be _Graph;
  assume G1 == G2;
  then G2 is reverseEdgeDirections of G1, {} by GLIB_009:42;
  hence thesis;
end;
