References
  
  [Bar09]   Barakat,   M.,   The   homalg   package   --   GAP4   (2007-2009),
  ((http://homalg.math.rwth-aachen.de/index.php/core-packages/homalg-package)).
  
  [BR06]  Barakat,  M.  and  Robertz,  D.,  homalg: First steps to an abstract
  package  for  homological  algebra,  in  Proceedings  of  the  X  meeting on
  computational  algebra  and  its  applications  (EACA 2006), Sevilla (Spain)
  (2006),                                                              29--32,
  ((http://homalg.math.rwth-aachen.de/maple/homalg_eaca06.pdf)).
  
  [BR08] Barakat, M. and Robertz, D., homalg -- A Meta-Package for Homological
  Algebra, J. Algebra Appl., 7, 3 (2008), 299--317, ((arXiv:math.AC/0701146)).
  
  [Gör08]      Görtzen,     S.,     GAP     Package     Gauss     (2007-2008),
  ((http://wwwb.math.rwth-aachen.de/goertzen/Gauss)).
  
  [LN08]  Lübeck,  F.  and  Neunhöffer,  M.,  GAP  Package GAPDoc (2007-2008),
  ((http://www.math.rwth-aachen.de/~Frank.Luebeck/GAPDoc)).