intro e_F
case e_nF
α : Type u_1
M : Matroid α
I B : Set α
Ys Xs : Set (Set α)
F : Set α
C : M.ModularCut
hC : C.Nonempty
e : α
he : e ∉ M.E
cl_eq_self : (C.extension e).cl F = F
e_not_mem : ¬(e ∈ F ∧ F \ {e} ∈ C)
M_eq : C.extension e ↾ M.E = M
f_not_mem : F \ {e} ∉ C
⊢ e ∉ F
case e_nF
α : Type u_1
M : Matroid α
I B : Set α
Ys Xs : Set (Set α)
F : Set α
C : M.ModularCut
hC : C.Nonempty
e : α
he : e ∉ M.E
cl_eq_self : (C.extension e).cl F = F
e_not_mem : ¬(e ∈ F ∧ F \ {e} ∈ C)
M_eq : C.extension e ↾ M.E = M
f_not_mem : F \ {e} ∉ C
e_F : e ∈ F
⊢ False