⊦ #oc(n, A, 0) = 1 ↔ (∃ m. m < 0 ∧ A[m] = n ∧ (∀ m1. m1 ≠ m ∧ m1 < 0 → A[m1] ≠ n))
[Concretesimprules((Csimpgen(nat freely generated by 0, +1;)))]