{C : Type u} →
  [inst : CategoryTheory.Category.{v, u} C] →
    {X Y : C} →
      {f : X ⟶ Y} →
        {motive : CategoryTheory.Mono f → Sort u_1} →
          ((right_cancellation :
                ∀ {Z : C} (g h : Z ⟶ X),
                  CategoryTheory.CategoryStruct.comp g f = CategoryTheory.CategoryStruct.comp h f → g = h) →
              motive ⋯) →
            (t : CategoryTheory.Mono f) → motive t