  An important way for describing groups is by finite presentations. Large
presentations arise in practice which are poorly suited for either human or
computer use. Presentation simplification processes which take bad
presentations and produce good presentations have been developed. Substantial
use is made of substring searching and appropriate techniques for this context
are described. Effective use is made of signatures and change flags. Change
flags are shown to be the most beneficial of the methods tested here, with very
significant performance improvement. Experimental performance figures are
given.
