The help system uses the Porter stemming algorithm to normalize words when building the full-text search index.

The Factor implementation of the algorithm is based on the Common Lisp version, which was hand-translated from ANSI C by Steven M. Haflich. The original ANSI C was written by Martin Porter.

A detailed description of the algorithm, along with implementations in various languages, can be at in

The main word of the algorithm takes an English word as input and outputs its stem:
stem ( str -- newstr )

The algorithm consists of a number of steps:
step1a ( str -- newstr )

step1b ( str -- newstr )

step1c ( str -- newstr )

step2 ( str -- newstr )

step3 ( str -- newstr )

step4 ( str -- newstr )

step5 ( str -- newstr )