# nLab interval object in chain complexes

## Theorems

#### Homological algebra

homological algebra

and

nonabelian homological algebra

diagram chasing

# Contents

## Idea

The standard interval object in a category of chain complexes in $R$Mod is an “abelianization” of the standard simplicial interval, the 1-simplex and a model of the unit interval, $[0,1]$, with the evident cell decomposition.

## Definition

Let $R$ be some ring and let $\mathcal{A} = R$Mod be the abelian category of $R$-modules. Write $Ch_\bullet(\mathcal{A})$ for the corresponding category of chain complexes.

###### Definition

The standard interval object in chain complexes

$I_\bullet \in Ch_\bullet(\mathcal{A})$

is the normalized chain complex of the simplicial chains on the simplicial 1-simplex:

$I_\bullet \coloneqq N_\bullet(C(\Delta[1])) \,.$

In components this means that

$I_\bullet = [ \cdots \to 0 \to 0 \to R \stackrel{(id,-id)}{\to} R \oplus R ] \,.$

## Properties

### Homotopies

###### Proposition

A homotopy with respect to $I_\bullet$ gives a chain homotopy and conversely.

See the entry on chain homotopy for more details.

Revised on September 3, 2012 13:21:36 by Tim Porter (95.147.237.93)