
theorem OPA:
  for a be non zero Integer holds Oddity (Parity a) = 1
  proof
  let a be non zero Integer;
  Parity (Parity a) = Parity a &
    (Parity(Parity a))*(Oddity(Parity a)) = Parity a;
  hence thesis by XCMPLX_1:7;
end;
