| n < # y ⊦ y = [], perm(y[n, a] -1l a, y -1l y[n]) |
⊦ perm(x, y) ↔ (∀ a. a ∈ x ∨ a ∈ y → #oc(a, x) = #oc(a, y))
n < # y ⊦ y = [], ∀ a0. a0 ∈ y[n, a] -1l a ∨ a0 ∈ y -1l y[n] → #oc(a0, y[n, a] -1l a) = #oc(a0, y -1l y[n])
Used terms: y -1l y[n], y[n, a] -1l a