exact add_le_add (M₁.r_mono inter_subset_right)
  (M₂.r_mono (diff_subset_diff_left hI₂.subset_ground))
α : Type u_1
M M₁ M₂ : Matroid α
A✝ I X E : Set α
inst✝¹ : M₁.FiniteRk
inst✝ : M₂.FiniteRk
hI₁ : M₁.Indep I
hI₂ : M₂.Indep I
A : Set α
⊢ M₁.r (I ∩ A) + M₂.r (I \ A) ≤ M₁.r A + M₂.r (M₂.E \ A)
no goals