| # x = n0 + n, n ≤ # x ⊦ firstn(n0, x) + lastn(n, x) = x |
# x = n0 + n ⊦ firstn(n0, x) + lastn(n, x) = x
Used simplifier rules: c: ⊦ m + n = n + m; from specification nat-basic2%a: ⊦ (m + n0) + n1 = m + n0 + n1; from specification nat-basic2%lep: ⊦ m ≤ m + n; from specification nat