no goals
α : Type u_1
β : α → Type ?u.46956
inst✝ : DecidableEq α
f g : Multiset α
⊢ Finset.card (Finset.Ioo f g) = ∏ i in toFinset f ∪ toFinset g, (count i g + 1 - count i f) - 2
rw [card_Ioo_eq_card_Icc_sub_two, card_Icc]