∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] [inst_1 : CategoryTheory.MonoidalCategory C] (M : C)
  [inst_2 : CategoryTheory.MonObj M],
  CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.whiskerLeft M CategoryTheory.MonObj.mul)
      CategoryTheory.MonObj.mul =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.associator M M M).inv
      (CategoryTheory.CategoryStruct.comp
        (CategoryTheory.MonoidalCategoryStruct.whiskerRight CategoryTheory.MonObj.mul M) CategoryTheory.MonObj.mul)