Theorem: Matroid.freeOn_contract (Matroid/Minor/Basic.lean)

State before:
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
⊢ freeOn E ／ X = freeOn (E \ X)
Tactic:
rw [← loopyOn_dual_eq, ← delete_dual_eq_dual_contract, loopyOn_delete, loopyOn_dual_eq]
State after:
no goals