nLab zigzag

Zigzags of morphisms

In a category $C$ a zigzag of morphisms is a finite collection of morphisms $(f_i)$ in $C$ of the form

$$\array{ && x_1 &&&& x_3 & \cdots \\ & {}^{\mathllap{f_1}}\swarrow && \searrow^{\mathrlap{f_2}} && {}^{\mathllap{f_3}}\swarrow && \searrow^{\mathrlap{f_4}} & \cdots \\ x_0 &&&& x_2 &&&& x_4 & \cdots } \,.$$

A zigzag consisting just out of two morphisms is a roof or span.

General such zig-zags of morphisms represent ordinary morphisms in the groupoidification of $C$ – the Kan fibrant replacement of its nerve, its simplicial localization or its 1-categorical localization at all its morphisms.

More generally, if in these zig-zags the left-pointing morphisms are restricted to be in a class $S \subset Mor(C)$, then these zig-zags represent morphisms in the simplicial localizaton or localization of $C$ at $S$.

Related concepts

• resolution, derived functor

• span, correspondence

• Burnside category

• zigzag persistence module