∀ {V : Type u} [inst : CategoryTheory.Category.{v, u} V] [inst_1 : CategoryTheory.Limits.HasZeroMorphisms V]
  (C : ChainComplex V ℕ) {X : V} (f : C.X 0 ⟶ X) (w : CategoryTheory.CategoryStruct.comp (C.d 1 0) f = 0) (i : ℕ),
  (C.truncateAugment f w).hom.f i = CategoryTheory.CategoryStruct.id (C.X i)