
theorem
  for a,b be positive Real holds [\a/]*[\b/] <= [\a*b/]
  proof
    let a,b be positive Real;
    [\a/]*[\b/] <= [\a/]*b <= a*b by PI1; then
    [\a/]*[\b/] <= a*b by XXREAL_0:2;
    hence thesis by INT_1:54;
  end;
