∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] [inst_1 : CategoryTheory.ChosenPullbacks C] {X : C}
  (R S T : CategoryTheory.Over X) {Z : C} (h : T.left ⟶ Z),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.associator R S T).inv.left
      (CategoryTheory.CategoryStruct.comp
        (CategoryTheory.ChosenPullbacksAlong.snd
          (CategoryTheory.CategoryStruct.comp (CategoryTheory.ChosenPullbacksAlong.snd R.hom S.hom) S.hom) T.hom)
        h) =
    CategoryTheory.CategoryStruct.comp
      (CategoryTheory.ChosenPullbacksAlong.snd R.hom (CategoryTheory.MonoidalCategoryStruct.tensorObj S T).hom)
      (CategoryTheory.CategoryStruct.comp (CategoryTheory.ChosenPullbacksAlong.snd S.hom T.hom) h)