| n ≤ # y ⊦ lastn(n, x + y) = lastn(n, y) |
∀ n, y. n ≤ # y → lastn(n, x0 + y) = lastn(n, y), n ≤ # y ⊦ lastn(n, (a + x0) + y) = lastn(n, y)
Used simplifier rules: list freely generated by [], +;;%Nil: ⊦ [] + x = x; from specification list%a: ⊦ (x + y) + z = x + y + z; from specification list