n ≤ #oc(a, a0 + x0), ∀ n, a. n ≤ #oc(a, x0) → n = 0 ∨ n = 1 ∨ dups(x0) ⊦ n = 1, n = 0, dups(a0 + x0)
Used simplifier rules: oc-e: ⊦ #oc(a, []) = 0;%list freely generated by [], +;;% ⊦ m ≤ 0 ↔ m = 0; (s)