theorem
  |{p,q,0.TOP-REAL 3}| = 0
  proof
    |{p,q,0.TOP-REAL 3}| = |(p, q <X> 0.TOP-REAL 3)| by EUCLID_5:def 5
                        .= |(p,0.TOP-REAL 3)| by Th42;
    hence thesis by EUCLID_2:32;
  end;
