∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.MonoidalCategory C]
  {R S : CategoryTheory.Mon C} (P : Bimod R S),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.whiskerRight (Bimod.regular R).actRight P.X)
      P.actLeft =
    CategoryTheory.CategoryStruct.comp
      (CategoryTheory.CategoryStruct.comp
        (CategoryTheory.MonoidalCategoryStruct.associator (Bimod.regular R).X R.X P.X).hom
        (CategoryTheory.MonoidalCategoryStruct.whiskerLeft (Bimod.regular R).X P.actLeft))
      P.actLeft