ins≤(a, []) = ins≤(a, y) ⊦ [] = y
∀ a, y. ins≤(a, x0) = ins≤(a, y) → x0 = y, ins≤(a, a0 + x0) = ins≤(a, y) ⊦ a0 + x0 = y
Used simplifier rules: list freely generated by [], +;;