UK TeX FAQ -- question label cancellation

### Cancelling terms in maths expressions

A technique used when explaining the behaviour of expressions or equations (often for pedagogical purposes). The cancel package provides several variants of cancellation marks (“`\`”, “`/`” and “`X`”), and a means of cancelling ‘to’ a particular value.

Documentation of cancel is in the package file.

`cancel.sty`
  macros/latex/contrib/cancel (or browse the directory); catalogue entry

This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=cancellation