exact (M.subset_cl _).trans
  (M.cl_subset_cl (inter_subset_right.trans subset_union_right))
α : Type u_1
M✝ M' N : Matroid α
e f : α
I J R B X✝ Y Z K C✝ C₁ C₂ : Set α
M : Matroid α
C X : Set α
⊢ M.E ∩ C ⊆ M.cl (X ∪ C)
no goals