| n0 ≤ m, (m + 1) + m0 < # x, m + m0 < # x, firstn(n0, restn(m0, x).rest) ⊑ firstn(m, restn(m0, x).rest), ∀ n1, m0, x. n1 + m0 < # x ∧ n0 ≤ n1 → x = [] ∨ firstn(n0, restn(m0, x).rest) ⊑ firstn(n1, restn(m0, x).rest) ⊦ x = [], firstn(n0, restn(m0, x).rest.rest) ⊑ firstn(m, restn(m0, x).rest.rest) |
⊦ x.rest = restn(1, x)
n0 ≤ m, (m + 1) + m0 < # x, m + m0 < # x, firstn(n0, restn(1, restn(m0, x))) ⊑ firstn(m, restn(1, restn(m0, x))), ∀ n1, m0, x. n1 + m0 < # x ∧ n0 ≤ n1 → x = [] ∨ firstn(n0, restn(m0, x).rest) ⊑ firstn(n1, restn(m0, x).rest) ⊦ x = [], firstn(n0, restn(1, restn(m0, x)).rest) ⊑ firstn(m, restn(1, restn(m0, x)).rest)
Used terms: restn(m0, x)