# Contents

## Definition

In any category, a cospan is a diagram like this:

$\begin{array}{ccccccc}& & a& & & & b\\ & & & {}_{f}↘& & {↙}_{g}& & \\ & & & & c& & & & \end{array}$\array{ && a &&&& b \\ & && {}_{f}\searrow & & \swarrow_g && \\ &&&& c &&&& }

A cospan in the category $C$ is the same as a span in the opposite category ${C}^{\mathrm{op}}$. So, all general facts about cospans in $C$ are general facts about spans in ${C}^{\mathrm{op}}$, and the reader may turn to the entry on spans to learn more.