rw [(hB.indep.diff {e}).not_mem_cl_iff (hB.subset_ground heB)]
case refine'_1
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
⊢ e ∉ M.cl (B \ {e})
case refine'_1
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.Indep (insert e (B \ {e})) ∧ e ∉ B \ {e}