
theorem
  for G being _Graph, W being Walk of G holds
    W is chordal iff W.reverse() is chordal
proof
  let G be _Graph, W be Walk of G;
  thus W is chordal implies W.reverse() is chordal by Lm3;
  assume W.reverse() is chordal;
  then W.reverse().reverse() is chordal by Lm3;
  hence thesis;
end;
