n = n0 + # x, # x ≤ n ⊦ firstn(m, restn(n, x + y)) = firstn(m, restn(n0, y))
Used simplifier rules: n ≤ m ⊦ n0 = m - n ↔ m = n0 + n; (elim) Used terms: n, # x, n0