m = m0 + 1, ('6' ' + '7' ' + '8' ' + '9' ')[m0] ' = "0", m < 5 ⊦ m = 0
Used simplifier rules: n ≠ 0 ⊦ m = n - 1 ↔ n = m + 1; (elim) Used terms: m, m0