
theorem
  for G1, G2 being _Graph, G being GraphUnion of G1, G2
  st G1 tolerates G2 holds G is GraphUnion of G2, G1
proof
  let G1, G2 be _Graph, G be GraphUnion of G1, G2;
  assume A1: G1 tolerates G2;
  then consider S being GraphUnionSet such that
    A2: S = {G1,G2} & G is GraphUnion of S by Def26;
  A3: G is Supergraph of G2 by A1, Th26;
  thus thesis by A1, A2, A3, Def26;
end;
