Theorem: Matroid.Basis.er_eq_encard (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
hIX : M.Basis I X
⊢ M.er X = I.encard
Tactic:
rw [← hIX.er, hIX.indep.er]
State after:
no goals