Xy-pic User's Guide

## 1.5 Breaks

It is also possible to "break" an arrow with a label using the `|` character: `\$\xymatrix@1{A\ar[r]``|``f&B}\$` will set .

If you just want an empty break you should use the special `\hole` break: the arrow was typeset by including `\$\xymatrix@1{ A\ar[r]``|``\hole & B }\$` in the text.

A different use of breaks is to place a label somewhere in a diagram outside the normal matrix mesh: this is accomplished by "breaking" an invisible arrow obtained using the `@{}` arrow style: the square

was typeset by

```\xymatrix{\ar @{} [dr] |{=}
A \ar[d] \ar[r] & B \ar[d] \\
B \ar[r]        & C        }```
There is more on breaks in section 2.7.

#### Exercise 4.

Typeset the first axiom of category theory as the display

Xy-pic User's Guide

© Kristoffer H. Rose <krisrose@brics.dk> December 19, 1996 / LaTeX2HTMLv96.1-h