Theorem: Matroid.Nonloop.er_eq (Matroid/Rank.lean)

State before:
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
he : M.Nonloop e
⊢ M.er {e} = 1
Tactic:
rw [← he.indep.basis_self.encard, encard_singleton]
State after:
no goals