| ⊦ n ≤ # x ∧ ¬ dups(x + y) → ¬ dups(firstn(n, x) + y) |
dups(firstn(n, x) + y), n ≤ # x ⊦ dups(x + y), dups(x), dups(y)
Used simplifier rules: a: ⊦ (x + y) + z = x + y + z; from specification list%a: ⊦ ¬ dups(x + y) → ¬ dups(x) ∧ ¬ dups(y); (forward) from specification list-dup