∀ {C : Type u} {X₁ Y₁ X₂ Y₂ : CategoryTheory.FreeMonoidalCategory C} (f : X₁.Hom Y₁) (g : X₂.Hom Y₂),
  CategoryTheory.FreeMonoidalCategory.HomEquiv (f.tensor g)
    ((f.whiskerRight X₂).comp (CategoryTheory.FreeMonoidalCategory.Hom.whiskerLeft Y₁ g))