-- Two topics are now equal if the word stems of their values are
equal. e.g. Two topics with values "cells" and "cell" are equal.
Note: The two topics, despite being equal, could contain different
information about the actions it performs. So, the two topics are
merged together.
-- Determiners and preterminers are erased from the values of Topics,
because the original (sentence) context of these parts-of-speech is
lost.

Signed off by: Mark Farrell<markfarr2011@gmail.com>