Theorem: Matroid.freeOn_r_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
E : Set α
hXE : X ⊆ E
⊢ (freeOn E).r X = X.ncard
Tactic:
rw [← er_toNat_eq_r, freeOn_er_eq hXE, ncard_def]
State after:
no goals