m < m0, n < n0, m0 * n0 ≤ m * n ⊦ m0 = 0, n0 = 0
Used simplifier rules: f: ⊦ m < n → n ≠ 0; (forward) from specification nat-basic1%lels: ⊦ ¬ m < n ↔ n ≤ m; from specification nat