theorem Th10:
  for h being Nat st h in HWZSet1(r) holds h > 0
   proof
     let h be Nat;
     assume h in HWZSet1(r); then
     ex h1 be Nat st h1 = h & ex p be Rational st
       p in HWZSet(r) & h1 = denominator(p);
     hence thesis;
   end;
