| m ≤ # x0, n ≤ # x0, ∀ m, n, a. m < # x0 ∧ n < # x0 → (a ∈ x0[m, x0[n]][n, x0[m]] ↔ a ∈ x0) ⊦ a ∈ (a0 ' + x0)[m, (a0 ' + x0)[n]][n, (a0 ' + x0)[m]] ↔ a ∈ a0 ' + x0 |
⊦ x ≠ [] ∧ n ≠ 0 → x[n] = x.tail[n - 1]
n ≤ # x0, m ≤ # x0, ∀ m, n, a. m < # x0 ∧ n < # x0 → (a ∈ x0[m, x0[n]][n, x0[m]] ↔ a ∈ x0) ⊦ a ∈ (a0 ' + x0)[m, (a0 ' + x0)[n]][n, (a0 ' + x0)[m]] ↔ a ∈ a0 ' + x0, a0 ' + x0 ≠ [] ∧ n ≠ 0
n ≤ # x0, m ≤ # x0, ∀ m, n, a. m < # x0 ∧ n < # x0 → (a ∈ x0[m, x0[n]][n, x0[m]] ↔ a ∈ x0) ⊦ a0 ' + x0 = [], a ∈ (a0 ' + x0)[m, (a0 ' + x0).tail[n - 1]][n, (a0 ' + x0)[m]] ↔ a ∈ a0 ' + x0, n = 0
Used terms: n, a0 ' + x0