∀ a0. (a0 = a ⊃ 1;0) + count(a0, bag) = 0 ⊦
Used simplifier rules: count-insert: ⊦ count(a, bag ++ b) = (a = b ⊃ 1;0) + count(a, bag);%count-empty: ⊦ count(a, ∅) = 0;