by Karel Dekimpe and Bettina Eick
The AClib package contains the almost crystallographic groups as classified by K. Dekimpe in the Springer Lecture Notes in Mathematics, Vol. 1639: "Almost-Bieberbach Groups: Affine and Polynomial Structures".
The groups are available as rational matrix groups. Further, all the groups in the library are polycyclic. If the Polycyclic package for computations with infinite polycyclic groups is installed, then polycyclic presentations for the almost crystallographic groups are available as well and can be used for computations with these groups.
Unpack the archive into the pkg directory of your GAP installation, or
into any directory listed in GAP's package search path, then load it with
gap> LoadPackage("aclib");
The manual is part of the package and is also available on the package homepage: https://gap-packages.github.io/aclib/
Please report any problems you encounter, and submit feature requests, via our issue tracker: https://github.com/gap-packages/aclib/issues
AClib is licensed under the Artistic License 2.0; see the file LICENSE for details.