English
Given a short exact sequence S of cochain complexes in an abelian category, there is a distinguished triangle in the derived category whose connecting morphism is δ related to S.
Русский
Для короткой точной последовательности SES коchain-комплекс в абелевой категории существует выделенный треугольник в производной категории, связывающийδ с SES.
LaTeX
$$$$ \triangleOfSESδ(hS) : \text{Triangle in DerivedCategory}(C) $$$$
Lean4
/-- The distinguished triangle in the derived category associated to a short
exact sequence of cochain complexes. -/
@[simps!]
noncomputable def triangleOfSES : Triangle (DerivedCategory C) :=
Triangle.mk (Q.map S.f) (Q.map S.g) (triangleOfSESδ hS)