Theorem: Matroid.contract_comm (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 C C₁✝ C₂✝ : Set α
M : Matroid α
C₁ C₂ : Set α
⊢ M ／ C₁ ／ C₂ = M ／ C₂ ／ C₁
Tactic:
rw [contract_contract, union_comm, contract_contract]
State after:
no goals