refine ⟨B, hB, ?_⟩
case intro.intro
ι : Type u_1
α : Type u_2
M : Matroid α
B✝ I J X X' Y Y' F : Set α
Xs Ys Js Is : ι → Set α
i j : ι
e f : α
hI : M.Indep I
hXs : ∀ (i : ι), Xs i ⊆ M.cl (Xs i ∩ I)
B : Set α
hB : M.Base B
hIB : I ⊆ B
⊢ M.ModularFamily Xs
case intro.intro
ι : Type u_1
α : Type u_2
M : Matroid α
B✝ I J X X' Y Y' F : Set α
Xs Ys Js Is : ι → Set α
i j : ι
e f : α
hI : M.Indep I
hXs : ∀ (i : ι), Xs i ⊆ M.cl (Xs i ∩ I)
B : Set α
hB : M.Base B
hIB : I ⊆ B
⊢ ∀ (i : ι), M.Basis (Xs i ∩ B) (Xs i)