| n ≤ # x0 + 1, dups(butlastn(n, a ' + x0)), ∀ n0. ¬ n0 ≤ # x0 ∨ ¬ dups(butlastn(n0, x0)) ⊦ a ∈ x0, dups(x0) |
⊦ n ≤ # x → butlastn(n, a ' + x) = a ' + butlastn(n, x)
¬ n ≤ # x0, n ≤ # x0 + 1, dups(butlastn(n, a ' + x0)), ∀ n0. ¬ n0 ≤ # x0 ∨ ¬ dups(butlastn(n0, x0)) ⊦ a ∈ x0, dups(x0)
n ≤ # x0, n ≤ # x0 + 1, dups(a ' + butlastn(n, x0)), ∀ n0. ¬ n0 ≤ # x0 ∨ ¬ dups(butlastn(n0, x0)) ⊦ a ∈ x0, dups(x0)
Used terms: x0, a, n