simp [← cl_inter_ground, singleton_inter_eq_empty.2 he,
  (show ¬ M.Nonloop e from fun h ↦ he h.mem_ground)]
case neg
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
he : e ∉ M.E
⊢ ¬M.Nonloop e ↔ M.cl {e} = M.cl ∅
no goals