
theorem Th26:
  for G1, G2 being _Graph, G being GraphUnion of G1, G2
  st G1 tolerates G2 holds G is Supergraph of G2
proof
  let G1, G2 be _Graph, G be GraphUnion of G1, G2;
  assume G1 tolerates G2;
  then consider S being GraphUnionSet such that
    A1: S = {G1,G2} & G is GraphUnion of S by Def26;
  G2 is Element of S by A1, TARSKI:def 2;
  then G2 is Subgraph of G by A1, Th21;
  hence thesis by GLIB_006:57;
end;
