
theorem
  for a be Integer, b be non zero Integer holds frac (b*frac (a/b)) = 0
  proof
    let a be Integer, b be non zero Integer;
    frac (b*frac (a/b)) = frac (b*(a/b)) by FR3
    .= frac a by XCMPLX_1:87;
    hence thesis;
  end;
