Changes by: Xin Yu (xiny at cs.caltech.edu)
Date: 2002-02-16 18:09:08 -0800 (Sat, 16 Feb 2002)
Revision: 3498
Log message:
Changed the definition of groups completely.
The former version is awkward for defining specific groups like
<Z, +> and is lack of generality since only ONE general group is
defined.
The current version adopts a parameter which makes it capable of
handling complicated situations.