
theorem
  for G being _Graph, W being Walk of G holds
    W is Trail-like iff len W = 2*(card W.edges())+1
proof
  let G be _Graph, W be Walk of G;
  set WE = W.edges(), WES = W.edgeSeq();
  W is Trail-like iff 2*card WE + 1 = 2*len WES+1 by FINSEQ_4:62;
  hence thesis by GLIB_001:def 15;
end;
