| ('7' ' + '8' ' + '9' ')[m] ' = "0", m < 3 ⊦ |
⊦ chars ≠ [] ∧ n ≠ 0 → chars[n] = chars.rest[n - 1]
¬('7' ' + '8' ' + '9' ' ≠ [] ∧ m ≠ 0), ('7' ' + '8' ' + '9' ')[m] ' = "0", m < 3 ⊦
'7' ' + '8' ' + '9' ' ≠ [] ∧ m ≠ 0, ('7' ' + '8' ' + '9' ').rest[m - 1] ' = "0", m < 3 ⊦
Used terms: m, '7' ' + '8' ' + '9' '