reserve G,G1,G2 for _Graph;
reserve W,W1,W2 for Walk of G;
reserve e,x,y,z for set;
reserve v for Vertex of G;
reserve n,m for Element of NAT;

theorem
  for W being Trail of G, e being set st e in W.last().edgesInOut() &
  not e in W.edges() holds W.addEdge(e) is Trail-like by Lm60;
