∀ a, y. (a = x0.last ∧ y = x0.butlast ↔ x0 = y + a ') ∨ x0 = [] ⊦ a0 + x0 = [], a = (a0 + x0).last ∧ y = (a0 + x0).butlast ↔ a0 + x0 = y + a '
Used simplifier rules: list freely generated by [], +;;