
theorem Th23:
  for G being _Graph for W1, W2 being Walk of G st W1.first() = W2
  .first() & not W1 is_a_prefix_of W2 holds len maxPrefix(W1,W2) +2 <= len W1
proof
  let G be _Graph, W1, W2 be Walk of G;
  assume W1.first() = W2.first() & not W1 c= W2;
  then len maxPrefix(W1,W2) < len W1 & len maxPrefix(W1,W2) is odd Nat by Th8
,Th22;
  hence thesis by CHORD:4;
end;
