Almost Crystallographic Groups - A Library and Algorithms

Version 1.3.2
Released 2020-01-28

This project is maintained by Bettina Eick

GAP Package AClib

The AClib package contains a library of almost crystallographic groups and a some algorithms to compute with these groups. A group is called almost crystallographic if it is finitely generated nilpotent-by-finite and has no non-trivial finite normal subgroups. Further, an almost crystallographic group is called almost Bieberbach if it is torsion-free. The almost crystallographic groups of Hirsch length 3 and a part of the almost cyrstallographic groups of Hirsch length 4 have been classified by Dekimpe. This classification includes all almost Bieberbach groups of Hirsch lengths 3 or 4. The AClib package gives access to this classification; that is, the package contains this library of groups in a computationally useful form. The groups in this library are available in two different representations. First, each of the groups of Hirsch length 3 or 4 has a rational matrix representation of dimension 4 or 5, respectively, and such representations are available in this package. Secondly, all the groups in this libraray are (infinite) polycyclic groups and the package also incorporates polycyclic presentations for them. The polycyclic presentations can be used to compute with the given groups using the methods of the Polycyclic package.

The current version of this package is version 1.3.2, released on 2020-01-28. For more information, please refer to the package manual. There is also a README file.


This package requires GAP version >=4.7

The following other GAP packages are needed:

The following additional GAP packages are not required, but suggested:


Karel Dekimpe, Bettina Eick.


For bug reports, feature requests and suggestions, please use the issue tracker.