theorem
  for G1, G2 being _Graph, V being set
  holds G2 is removeVertices of G1, V iff
    G2 is removeVertices of G1, V /\ the_Vertices_of G1
proof
  let G1, G2 be _Graph, V be set;
  the_Vertices_of G1 \ V = the_Vertices_of G1 \ (V /\ the_Vertices_of G1)
    by XBOOLE_1:47;
  hence thesis;
end;
