
theorem Th21:
  for G1, G2 being _Graph, F being PGraphMapping of G1, G2
  st F_V is one-to-one & rng F_E = the_Edges_of G2 holds F is continuous
proof
  let G1, G2 be _Graph, F be PGraphMapping of G1, G2;
  assume A1: F_V is one-to-one & rng F_E = the_Edges_of G2;
  then F is semi-continuous by Th17;
  hence thesis by A1, Th19;
end;
