| a ∈ y ⊦ #oc(a, filter(x, y)) = #oc(a, x) |
∀ a, y. a ∈ y → #oc(a, filter(x0, y)) = #oc(a, x0), a ∈ y ⊦ #oc(a, filter(a0 + x0, y)) = #oc(a, a0 + x0)
Used simplifier rules: oc-e: ⊦ #oc(a, []) = 0;%list freely generated by [], +;;%filt-e: ⊦ filter([], y) = []; from specification list-set