
theorem Th145:
  for G1 being _Graph, G2 being DSimpleGraph of G1
  holds G1 is chordal iff G2 is chordal
proof
  let G1 be _Graph, G2 be DSimpleGraph of G1;
  consider H being removeDParallelEdges of G1 such that
    A1: G2 is removeLoops of H by Th120;
  H is chordal iff G2 is chordal by A1, Th65;
  hence thesis by Th107;
end;
