Theorem: Matroid.er_eq_coe_iff (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
inst✝ : M.FiniteRk
n : ℕ
⊢ M.er X = ↑n ↔ M.r X = n
Tactic:
rw [← coe_r_eq, Nat.cast_inj]
State after:
no goals