References
  
  [Bar09]   Barakat,   M.,   The   homalg   package   --   GAP4   (2007-2009),
  ((http://homalg.math.rwth-aachen.de/index.php/core-packages/homalg-package)).
  
  [BGKLH08]  Barakat,  M., Görtzen, S., Kirschmer, M. and Lange-Hegermann, M.,
  GAP              Package             RingsForHomalg             (2007-2008),
  ((http://homalg.math.rwth-aachen.de/index.php/core-packages/ringsforhomalg)).
  
  [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)).
  
  [Gör08a]    Görtzen,    S.,    GAP   Package   GaussForHomalg   (2007-2008),
  ((http://wwwb.math.rwth-aachen.de/goertzen/GaussForHomalg)).
  
  [Gör08b]      Görtzen,      S.,     GAP     Package     SCO     (2007-2008),
  ((http://wwwb.math.rwth-aachen.de/goertzen/SCO)).
  
  [ht09]    homalg    team,    T.,    The    homalg    project    (2003-2009),
  ((http://homalg.math.rwth-aachen.de/)).
  
  [LN08]  Lübeck,  F.  and  Neunhöffer,  M.,  GAP  Package GAPDoc (2007-2008),
  ((http://www.math.rwth-aachen.de/~Frank.Luebeck/GAPDoc)).
  
  [MP99]  Moerdijk,  I.  and Pronk, D. A., Simplicial cohomology of orbifolds,
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