∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] [inst_1 : CategoryTheory.Limits.HasPullbacks C] {X : C}
  (Y : CategoryTheory.Over X),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.leftUnitor Y).inv.left
      (CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.id X) Y.hom) =
    Y.hom