∀ m, n. # x0 = m + 1 ∧ n ≤ m → #(x0 -1l n) = m ∨ x0 = [], #(a + x0) = m + 1, n ≤ m ⊦ #((a + x0) -1l n) = m, a + x0 = []
Used simplifier rules: list freely generated by [], +;;