7 Development History
  
  
  7.1 Versions of the Package
  
  The  first  version,  GraphGpd  1.001,  formed  part  of Emma Moore's thesis
  [Moo01] in December 2000, but was not made generally available.
  
  Version 1.002 of GraphGpd was prepared to run under GAP 4.4 in January 2004;
  was  submitted  to  the GAP council to be considered as an accepted package;
  but suggestions from the referee were not followed up.
  
  In  April  2006  the  manual was converted to GAPDoc format. Variables Star,
  Costar  and  CoveringGroup  were  found  to  conflict  with  usage  in other
  packages,     and     were     renamed    VertexStar,    VertexCostar    and
  CoveringGroupOfGroupoid respectively. Similarly, the Vertices and Arcs of an
  FpWeightedDigraph were changed from attributes to record components.
  
  In the spring of 2006 the package was extensively rewritten and renamed Gpd.
  Version  1.01  was  submitted  as  a deposited package in June 2006. Version
  1.03,  of October 2007, fixed some file protections, and introduced the test
  file gpd_manual.tst.
  
  Version  1.05,  of November 2008, was released because the website at Bangor
  changed.
  
  A  further extensive rewrite is in progress, introducing magmas with objects
  and  their  mappings, but many of the functions fail to work at present, and
  this manual is far from correct.
  
  
  7.2 What needs to be done next?
  
  Computationally, there are three types of connected groupoid:
  
  --    those with identical object groups,
  
  --    those with object groups conjugate in some supergroup,
  
  --    those with object groups which are simply isomorphic.
  
  GraphGpd  attempted  to  implement  the second case, while Gpd 1.01 and 1.03
  considered  only  the  first  case, and Gpd 1.05 extended 1.03 to the second
  case. Here are some other immediate requirements:
  
  --    Automorphism group of a groupoid.
  
  --    normal subgroupoids and quotient groupoids;
  
  --    more  methods  for morphisms of groupoids, particularly when the range
        is not connected;
  
  --    ImageElm  and ImagesSource for the cases of groupoid morphisms not yet
        covered;
  
  --    Enumerator for IsHomsetCosetsRep;
  
  --    free groupoid on a graph;
  
  --    methods   for   FreeProductWithAmalgamation   and   HnnEntension   for
        pc-groups;
  
  --    convert      GraphOfGroupsRewritingSystem      to     the     category
        IsRewritingSystem;
  
  --    in XMod, implement crossed modules over groupoids.