n ≤ #oc(a, x) ⊦ n = 0, n = 1, dups(x)
Used simplifier rules: ⊦ 1 < m ↔ ¬(m = 0 ∨ m = 1); (s)% ⊦ m ≤ n ↔ ¬ n < m; (ss)