
theorem
  for G1, G2 being _Graph, F being PGraphMapping of G1, G2
  for v being Vertex of G1 st F is Disomorphism holds
    F_E.:(v.edgesIn()) = (F_V/.v).edgesIn() &
    F_E.:(v.edgesOut()) = (F_V/.v).edgesOut()
proof
  let G1, G2 be _Graph, F be PGraphMapping of G1, G2;
  let v be Vertex of G1;
  assume A1: F is Disomorphism;
  then dom F_V = the_Vertices_of G1 by GLIB_010:def 11;
  hence thesis by A1, Th89;
end;
