exact ⟨M.ground_nonempty.some, M.ground_nonempty.some_mem,
  hI.subset_cl.trans ((M.cl_subset_cl (empty_subset _)))⟩
case refine'_1.intro.inl
α : Type u_1
ι : Type u_2
M N : Matroid α
I B X X' Y Y' Z R : Set α
n : ℕ∞
e f : α
inst✝ : M.Nonempty
hX : autoParam (X ⊆ M.E) _auto✝
hI : M.Basis ∅ X
⊢ ∃ e ∈ M.E, X ⊆ M.cl {e}
no goals