
theorem
  for G1 being _Graph, E being set, G2 being reverseEdgeDirections of G1, E
  holds G2 is G1-isomorphic
proof
  let G1 be _Graph, E be set, G2 be reverseEdgeDirections of G1, E;
  consider F being PGraphMapping of G1, G2 such that
    A1: F = id G1 & F is isomorphism by Th83;
  thus thesis by A1, GLIB_010:def 23;
end;
