∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Preadditive C] {P Q R : C} (f : P ⟶ Q)
  (g : Q ⟶ R) [CategoryTheory.IsIso f], (CategoryTheory.CategoryStruct.comp f g = 0) = (g = 0)