rw [← hIX.eq_of_subset_indep (hB.indep.inter_left X) (inter_subset_inter_right _ hIB)
  inter_subset_left, ← hIY.eq_of_subset_indep (hB.indep.inter_left Y)
  (inter_subset_inter_right _ hIB) inter_subset_left]
case refine_2
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
M : Matroid α
X Y : Set α
x✝ : ∃ I, (∃ B, M.Base B ∧ I ⊆ B) ∧ M.Basis (X ∩ I) X ∧ M.Basis (Y ∩ I) Y
I B : Set α
hB : M.Base B
hIB : I ⊆ B
hIX : M.Basis (X ∩ I) X
hIY : M.Basis (Y ∩ I) Y
⊢ M.Basis (Y ∩ B) Y ∧ M.Basis (X ∩ B) X
case refine_2
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
M : Matroid α
X Y : Set α
x✝ : ∃ I, (∃ B, M.Base B ∧ I ⊆ B) ∧ M.Basis (X ∩ I) X ∧ M.Basis (Y ∩ I) Y
I B : Set α
hB : M.Base B
hIB : I ⊆ B
hIX : M.Basis (X ∩ I) X
hIY : M.Basis (Y ∩ I) Y
⊢ M.Basis (Y ∩ I) Y ∧ M.Basis (X ∩ I) X