Theorem: Matroid.rFin_insert_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
⊢ M.rFin (insert e X) ↔ M.rFin X
Tactic:
rw [← singleton_union, (M.rFin_singleton e).rFin_union_iff]
State after:
no goals