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

Answer.

 

Xy-pic User's Guide