no goals
α : Type u_1
inst✝ : DecidableEq α
𝒜✝ ℬ✝ : Finset (Finset α)
s : Finset α
a✝ a : α
𝒜 ℬ : Finset (Finset α)
⊢ memberSubfamily a (𝒜 ∪ ℬ) = memberSubfamily a 𝒜 ∪ memberSubfamily a ℬ
simp_rw [memberSubfamily, filter_union, image_union]