  Diff is a software program that detects differences between two data sets and
is useful in natural language processing. This paper shows several examples of
the application of diff. They include the detection of differences between two
different datasets, extraction of rewriting rules, merging of two different
datasets, and the optimal matching of two different data sets. Since diff comes
with any standard UNIX system, it is readily available and very easy to use.
Our studies showed that diff is a practical tool for research into natural
language processing.
