simpa [insert_eq_of_mem heB] using hB.cl_eq.symm
case refine'_2
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
hB : M.Base B
heB : e ∈ B
⊢ M.E = M.cl (insert e (M.cl (B \ {e})))
no goals