
theorem
  for G being _Graph, W being Walk of G holds len W.vertexSeq() = W.length()+1
proof
  let G be _Graph, W be Walk of G;
  2*len W.vertexSeq() = len W +1 by GLIB_001:def 14
    .= 2*W.length()+1 +1 by GLIB_001:112
    .= 2*(W.length()+1);
  hence thesis;
end;
