
theorem Th28:
  for G being _Graph, W1,W2 being Walk of G st
    W1.last() = W2.first() holds
      W1.append(W2).length() = W1.length() + W2.length()
proof
  let G being _Graph, P,H being Walk of G;
  assume H.first() = P.last();
  hence P.append(H).length() = len (P.edgeSeq() ^ H.edgeSeq()) by GLIB_001:85
    .= P.length() + H.length() by FINSEQ_1:22;
end;
