exact union_subset (subset_iUnion _ _) (subset_iUnion _ _)
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, Is i)
hdj : Pairwise (Disjoint on Is)
hIs : ∀ (i : ι), M.Basis (Is i) (Xs i)
i j : ι
hij : i ≠ j
⊢ Is i ∪ Is j ⊆ ⋃ i, Is i
no goals