| ¬ n < # a0 ', a ∈ x0, n ≤ # x0, ∀ n0, a1. n0 < # x0 → (a1 ∈ x0 -1l n0 ↔ a1 ≠ x0[n0] ∧ a1 ∈ x0) ⊦ x0 = [], a = x0[n - # a0 '], a ∈ (a0 ' + x0) -1l n, a0 ∈ x0, dups(x0) |
a ∈ x0, n ≤ # x0, ∀ n0, a1. n0 < # x0 → (a1 ∈ x0 -1l n0 ↔ a1 ≠ x0[n0] ∧ a1 ∈ x0) ⊦ x0 = [], a = x0[n - 1], n = 0, a ∈ (a0 ' + x0) -1l n, a0 ∈ x0, dups(x0)
Used simplifier rules: one-01: ⊦ m < 1 ↔ m = 0; from specification nat-basic1%len-02: ⊦ # a ' = 0 +1; from specification list