∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.MonoidalCategory C]
  (X Y Z : CategoryTheory.Center C) (U : C),
  CategoryTheory.CategoryStruct.comp
      (CategoryTheory.MonoidalCategoryStruct.whiskerRight
        (CategoryTheory.MonoidalCategoryStruct.associator X.fst Y.fst Z.fst).hom U)
      ((X.tensorObj (Y.tensorObj Z)).snd.β U).hom =
    CategoryTheory.CategoryStruct.comp (((X.tensorObj Y).tensorObj Z).snd.β U).hom
      (CategoryTheory.MonoidalCategoryStruct.whiskerLeft U
        (CategoryTheory.MonoidalCategoryStruct.associator X.fst Y.fst Z.fst).hom)