rw [hI.er_eq_encard, loopyOn_indep_iff.1 hI.indep, encard_empty]
case intro
α : Type u_1
ι : Type u_2
M N : Matroid α
I✝ B X✝ X' Y Y' Z R : Set α
n : ℕ∞
e f : α
E✝ E X I : Set α
hI : (loopyOn E).Basis' I X
⊢ (loopyOn E).er X = 0
no goals