rw [← M.cl_union_loops_eq (X \ M.cl ∅), diff_union_self, cl_union_cl_right_eq, union_empty]
α : Type u_1
β : Type u_2
M✝ N : Matroid α
e f : α
B L L' I X✝ Y Z F C K : Set α
M : Matroid α
X : Set α
⊢ M.cl (X \ M.cl ∅) = M.cl X
no goals