simp [ExtIndep, he.mem_cl_iff_mem, ModularCut.mem_delete_elem_iff]
case h.a
α : Type u_1
M : Matroid α
I J B F₀ F F' X Y : Set α
e f : α
U✝ U : M.ModularCut
hI : U.ExtIndep e I
hInmax : I ∉ maximals (fun x x_1 => x ⊆ x_1) {I | U.ExtIndep e I}
hBmax : B ∈ maximals (fun x x_1 => x ⊆ x_1) {I | U.ExtIndep e I}
he : M.Coloop e
x✝ : Set α
⊢ (U.delete {e}).ExtIndep e x✝ ↔ U.ExtIndep e x✝
no goals