rw [contract_spanning_iff', inter_eq_self_of_subset_left hC]
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
hC : autoParam (C ⊆ M.E) _auto✝
⊢ (M ／ C).Spanning X ↔ M.Spanning (X ∪ C) ∧ Disjoint X C
no goals