rw [← dual_delete_dual_eq_contract, ← dual_delete_dual_eq_contract, dual_inj,
  delete_eq_delete_iff, dual_ground]
α : Type u_1
M M' N : Matroid α
e f : α
I J R B X Y Z K C C₁ C₂ : Set α
⊢ M ／ C₁ = M ／ C₂ ↔ C₁ ∩ M.E = C₂ ∩ M.E
no goals