  
  [1X1. Introduction[0X
  
  Groupoids  are  mathematical  categories in which every arrow is invertible.
  The  [5XGpd[0X  package  provides functions for the computation with groupoids and
  their  morphisms;  for graphs of groups and graphs of groupoids. The package
  is far from complete, and development continues.
  
  It  was  used  by Emma Moore in her thesis [Moo01] to calculate normal forms
  for  Free  Products  with  Amalgamation,  and  for  HNN-extensions, when the
  initial groups have rewrite systems.
  
  [5XGpd[0X  is implemented using [5XGAP[0X 4.4. Some of the utility functions in the [5XXMod[0X
  package for crossed modules are used.
  
  The  information  parameter  [10XInfoGpd[0X  takes  default  value [10X1[0X which, for the
  benefit of new users, causes more messages to be printed out when operations
  fail.  When raised to a higher value, additional information is printed out.
  Help is available in the usual way.
  
  [4X---------------------------  Example  ----------------------------[0X
    [4X[0X
    [4Xgap> LoadPackage( "gpd" );[0X
    [4X------------------------------------------------------------[0X
    [4Xloading XMod 2.010 for GAP 4.4 - Murat Alp and Chris Wensley[0X
    [4X------------------------------------------------------------[0X
    [4X-----------------------------------------------------------[0X
    [4Xloading Gpd 1.03 for GAP 4.4 - Emma Moore and Chris Wensley[0X
    [4X-----------------------------------------------------------[0X
    [4Xtrue[0X
    [4Xgap> ?Groupoid[0X
    [4XHelp: several entries match this topic - type ?2 to get match [2][0X
    [4X[0X
    [4X[1] Gpd: Groupoid[0X
    [4X[2] loops (not loaded): groupoid[0X
    [4X[3] Gpd: Groupoids[0X
    [4X[4] Gpd: Groupoids: their elements and attributes[0X
    [4X[5] Gpd: GroupoidByUnion[0X
    [4X[6] Gpd: GroupoidElement[0X
    [4X[7] Gpd: GroupoidMorphismWithCommonRange[0X
    [4X[8] Gpd: GroupoidMorphism[0X
    [4X[9] Gpd: GroupoidMorphismByComponents[0X
    [4X[10] Gpd: GroupoidMorphismByUnion[0X
    [4X[11] Gpd: GroupoidsOfGraphOfGroupoids[0X
    [4X[0X
  [4X------------------------------------------------------------------[0X
  
  Once the package is loaded, it is possible to check the correct installation
  by  running  the  test suite of the package with the following command. (The
  test file itself is [11Xtst/gpd_manual.tst[0X.)
  
  [4X---------------------------  Example  ----------------------------[0X
    [4X[0X
    [4Xgap> ReadPackage( "gpd", "tst/testall.g" );[0X
    [4X+ Testing all example commands in the Gpd manual[0X
    [4X+ GAP4stones: 0[0X
    [4Xtrue[0X
    [4X[0X
  [4X------------------------------------------------------------------[0X
  
  You may reference this package by mentioning [BMPW02] and [Moo01].
  
