∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.MonoidalCategory C]
  [inst_2 : CategoryTheory.BraidedCategory C] (X Y : CategoryTheory.Mon C),
  CategoryTheory.MonoidalCategoryStruct.whiskerLeft X (CategoryTheory.CategoryStruct.id Y) =
    CategoryTheory.CategoryStruct.id (CategoryTheory.MonoidalCategoryStruct.tensorObj X Y)