∀ (C : Type u) [inst : CategoryTheory.Category.{v, u} C] (F G H : CategoryTheory.Functor C C) (X : C),
  (CategoryTheory.MonoidalCategoryStruct.associator F G H).hom.app X =
    CategoryTheory.CategoryStruct.id
      ((CategoryTheory.MonoidalCategoryStruct.tensorObj (CategoryTheory.MonoidalCategoryStruct.tensorObj F G) H).obj X)