| a ∈ firstn(n, a0 ' + x0), n ≤ pos(a, a0 ' + x0), ∀ a1, n0. ¬ a1 ∈ firstn(n0, x0) ∨ ¬ n0 ≤ pos(a1, x0) ⊦ |
n = n1 +1, a ∈ firstn(n, a0 ' + x0), n ≤ pos(a, a0 ' + x0), ∀ a1, n0. ¬ a1 ∈ firstn(n0, x0) ∨ ¬ n0 ≤ pos(a1, x0) ⊦
Used simplifier rules: nat freely generated by 0, +1;;% ⊦ 0 ≤ m; (s)% ⊦ firstn(0, x) = []; (s)% ⊦ ¬ a ∈ []; (s)