| n < m, m ≤ # x, n < # x ⊦ firstn(m, x)[n] = x[n], m = 0, x = [] |
∀ n, m. n < m ∧ m ≤ # x0 ∧ n < # x0 → firstn(m, x0)[n] = x0[n] ∨ m = 0 ∨ x0 = [], n < m, m ≤ #(a + x0), n < #(a + x0) ⊦ firstn(m, a + x0)[n] = (a + x0)[n], m = 0, a + x0 = []
Used simplifier rules: list freely generated by [], +;;