ext b
α : Type u_1
β : Type u_2
inst✝¹ : DecidableEq α
inst✝ : DecidableEq β
s1 s2 : Finset α
f : α → Finset β
⊢ Finset.biUnion (s1 ∪ s2) f = Finset.biUnion s1 f ∪ Finset.biUnion s2 f
case a
α : Type u_1
β : Type u_2
inst✝¹ : DecidableEq α
inst✝ : DecidableEq β
s1 s2 : Finset α
f : α → Finset β
b : β
⊢ b ∈ Finset.biUnion (s1 ∪ s2) f ↔ b ∈ Finset.biUnion s1 f ∪ Finset.biUnion s2 f