reserve G, G2 for _Graph, V, E for set,
  v for object;

theorem Th15:
  for G2, E for G1 being reverseEdgeDirections of G2, E, W1 being Walk of G1
  holds W1 is Walk of G2
proof
  let G2, E;
  let G1 be reverseEdgeDirections of G2, E;
  let W1 be Walk of G1;
  reconsider G3 = G2 as reverseEdgeDirections of G1, E by Th3;
  W1 is Walk of G3 by Th14;
  hence thesis;
end;
