x = a0 + y, ordered≤(x) ⊦ ins≤(a, x) = a0 ' + ins≤(a, y), x = [], a < a0
Used simplifier rules: x ≠ [] ⊦ a = x.head ∧ y = x.tail ↔ x = a + y; (elim) Used terms: x, a0, y