<Chapter Label="Introduction">
<Heading>Introduction</Heading>
<Index>cryst</Index>
<P/>
The &Cryst; package, previously known as <Package>CrystGAP</Package>, provides 
functions for the computation with affine crystallographic groups, 
in particular space groups. For the definition of the standard 
crystallographic notions we refer to the International Tables 
<Cite Key="Hah95"/>, in particular the chapter by Wondratschek <Cite Key="Won95"/>,
and to the introductory chapter in <Cite Key="BBNWZ78"/>. The principal 
algorithms used in this package are described in <Cite Key="EGN97"/>.
<P/>
The present version for &GAP;&nbsp;4 has been considerably reworked from
an earlier version for &GAP;&nbsp;3.4.4. Most of the porting to &GAP;&nbsp;4
has been done by Franz Gähler. Besides affine crystallographic
groups acting from the right, also affine crystallographic groups acting 
from the left are now fully supported. Many algorithms have been added, 
extended, or improved in other ways.
<P/>
Our warmest thanks go to Max Neunhöffer, whose extensive
testing of the &GAP; 4 version of &Cryst; in connection with &XGAP; 
uncovered several bugs and led to many performance improvements.
<P/>
&Cryst; is implemented in the &GAP;&nbsp;4 language, and runs on any 
system supporting &GAP;&nbsp;4. However, certain commands may require 
that other &GAP; packages such as &CaratInterface; or &XGAP; are installed.
In particular, the routines in Section&nbsp;<Ref Sect="Normalizers"/> are likely
to require &CaratInterface;, and the function WyckoffGraph (see&nbsp;<Ref Func="WyckoffGraph"/>)
requires &XGAP;. Both &CaratInterface; and &XGAP; may be available
only under Unix.
<P/>
The &Cryst; package is loaded with the command
<Example><![CDATA[
gap> LoadPackage( "cryst" ); 
true
]]></Example>
For bug reports, suggestions and comments please use
the issue tracker on GitHub:
<P/>
<URL>https://github.com/gap-packages/Cryst/issues/</URL>
</Chapter>
