simp_rw [eq_loopyOn_iff_cl, contract_cl_eq, empty_union, loopyOn_cl_eq, contract_ground,
  loopyOn_ground, true_and]
α : Type u_1
M M' N : Matroid α
e f : α
I J R B X✝ Y Z K E✝ E X : Set α
⊢ loopyOn E ／ X = loopyOn (E \ X)
no goals