rw [← cl_biUnion_cl_eq_cl_biUnion, iUnion₂_congr h, cl_biUnion_cl_eq_cl_biUnion]
α : Type u_1
ι : Type u_2
M✝ : Matroid α
F I J X Y B C R : Set α
e f x y : α
M : Matroid α
Xs Ys : ι → Set α
A : Set ι
h : ∀ i ∈ A, M.cl (Xs i) = M.cl (Ys i)
⊢ M.cl (⋃ i ∈ A, Xs i) = M.cl (⋃ i ∈ A, Ys i)
no goals