m ≤ m0 + n0, n0 < n1, m0 + n1 ≤ m ⊦ n1 = 0
Used simplifier rules: lels: ⊦ ¬ m < n ↔ n ≤ m;%f: ⊦ m < n → n ≠ 0; (forward) from specification nat-basic1