simp only [hB.mem_coloop_iff_forall_not_mem_fundCct (.inr hfI), mem_diff, mem_insert_iff, not_or,
  and_imp, not_forall, Classical.not_imp, not_not, exists_prop, exists_and_left] at hf
α : Type u_1
M : Matroid α
C K : Set α
e f g : α
I : Set α
hI : M.Indep I
hI' : M.Hyperplane I
heI : e ∈ M.E \ I
hfI : f ∈ I
hf : ¬M.Coloop f
hB : M.Base (insert e I)
⊢ M.ConnectedTo e f
α : Type u_1
M : Matroid α
C K : Set α
e f g : α
I : Set α
hI : M.Indep I
hI' : M.Hyperplane I
heI : e ∈ M.E \ I
hfI : f ∈ I
hB : M.Base (insert e I)
hf : ∃ x ∈ M.E, ¬x = e ∧ x ∉ I ∧ f ∈ M.fundCct x (insert e I)
⊢ M.ConnectedTo e f