| n < pos(a, a0 ' + x0), n < m, a ∈ firstn(n, a0 ' + x0), m ≤ pos(a, a0 ' + x0), ∀ n0, m0, a1. ¬ n0 < m0 ∨ ¬ n0 < pos(a1, x0) ∨ ¬ a1 ∈ firstn(n0, x0) ∨ ¬ m0 ≤ pos(a1, x0) ⊦ |
n = n1 +1, n < m, n < pos(a, a0 ' + x0), a ∈ firstn(n, a0 ' + x0), m ≤ pos(a, a0 ' + x0), ∀ n0, m0, a1. ¬ n0 < m0 ∨ ¬ n0 < pos(a1, x0) ∨ ¬ a1 ∈ firstn(n0, x0) ∨ ¬ m0 ≤ pos(a1, x0) ⊦
Used simplifier rules: nat freely generated by 0, +1;;% ⊦ firstn(0, x) = []; (s)% ⊦ ¬ a ∈ []; (s)