| n + m ≤ m0, n0 + m0 ≤ 1 + # x0, ∀ n0, m0, n, m. n0 + m0 ≤ # x0 ∧ n + m ≤ m0 → firstn(m, restn(n, firstn(m0, restn(n0, x0)))) = firstn(m, restn(n0 + n, x0)) ⊦ firstn(m, restn(n, firstn(m0, restn(n0, a ' + x0)))) = firstn(m, restn(n0 + n, a ' + x0)) |
⊦ 0 < n → restn(n, x) = restn(n -1, x.tail)
n0 + m0 ≤ 1 + # x0, n + m ≤ m0, ∀ n0, m0, n, m. n0 + m0 ≤ # x0 ∧ n + m ≤ m0 → firstn(m, restn(n, firstn(m0, restn(n0, x0)))) = firstn(m, restn(n0 + n, x0)) ⊦ firstn(m, restn(n, firstn(m0, restn(n0, a ' + x0)))) = firstn(m, restn(n0 + n, a ' + x0)), 0 < n0
0 < n0, n0 + m0 ≤ 1 + # x0, n + m ≤ m0, ∀ n0, m0, n, m. n0 + m0 ≤ # x0 ∧ n + m ≤ m0 → firstn(m, restn(n, firstn(m0, restn(n0, x0)))) = firstn(m, restn(n0 + n, x0)) ⊦ firstn(m, restn(n, firstn(m0, restn(n0 -1, (a ' + x0).tail)))) = firstn(m, restn(n0 + n, a ' + x0))
Used terms: a ' + x0, n0