rw [contract_loops_eq, diff_eq_empty] at h
α : Type u_1
M N : Matroid α
e f g : α
I X P D C : Set α
hC : (M ↾ C).cl ∅ = ∅
h : (M ／ C).cl ∅ = ∅
⊢ M.cl ∅ = ∅
α : Type u_1
M N : Matroid α
e f g : α
I X P D C : Set α
hC : (M ↾ C).cl ∅ = ∅
h : M.cl C ⊆ C
⊢ M.cl ∅ = ∅