rw [contract_elem, flat_contract_iff, union_singleton, disjoint_singleton_right]
α : Type u_1
M : Matroid α
I F X Y F' F₀ F₁ F₂ P L H H₁ H₂ H' B C K : Set α
e f : α
he : M.Nonloop e
⊢ (M ／ e).Flat F ↔ M.Flat (insert e F) ∧ e ∉ F
no goals