| #oc(a, x) = #oc(a, x) - 1, a ∈ x, perm(x -1l a, x), ∀ a0. a0 ∈ x ∨ a0 ∈ x -1l a → #oc(a0, x) = #oc(a0, x -1l a) ⊦ |
Used simplifier rules: in-05: ⊦ a ∈ x → #oc(a, x) ≠ 0;%eq: ⊦ m = m + n ↔ n = 0; from specification nat-basic2%a: ⊦ (m + n0) + n1 = m + n0 + n1; from specification nat-basic2%c: ⊦ m + n = n + m; from specification nat-basic2%n ≠ 0 ⊦ m = n - 1 ↔ n = m + 1; (elim) Used terms: #oc(a, x), m