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<?xml version="1.0" encoding="UTF-8"?>

<Chapter Label="chap-history">
<Heading>Development History</Heading>

<Section Label="sec-versions">
<Heading>Versions of the Package</Heading>

The first version, <Package>GraphGpd</Package> 1.001,
formed part of Emma Moore's thesis in December 2000,
but was not made generally available.
<P/>
Version 1.002 of <Package>GraphGpd</Package>
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.
<P/>
In April 2006 the manual was converted to <Package>GAPDoc</Package> format.
Variables <C>Star</C>, <C>Costar</C> and <C>CoveringGroup</C> were
found to conflict with usage in other packages, and were renamed
<C>VertexStar</C>, <C>VertexCostar</C> and
<C>CoveringGroupOfGroupoid</C> respectively.
Similarly, the <C>Vertices</C> and <C>Arcs</C> of an <C>FpWeightedDigraph</C>
were changed from attributes to record components.
<P/>
In the spring of 2006 the package was extensively rewritten
and renamed <Package>Gpd</Package>.
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 <F>gpd_manual.tst</F>.
<P/>
Version 1.05, of November 2008, was released when the website
at Bangor changed.
<P/>
Since then, the package has been rewritten again,
introducing magmas with objects and their mappings.
Functions to implement constructions contained in <Cite Key="AlWe" />
have been added, but this is ongoing work.
<P/>
Versions 1.09 to 1.15 were prepared for the anticipated release of &GAP; 4.5
in June 2012.
<P/>
<Package>Gpd</Package> became an accepted &GAP; package in May 2015.
<P/>
In April 2017 the package was renamed again, as <Package>groupoids</Package>.
<P/>
In August 2017 the implementation of groupoid homomorphisms was completely
revised with the emphasis now on a mapping from a set of generating arrows
to their images.
<P/>
In September 2017 various functions were revised so that, at last,
the operation <C>DiscreteNormalPreXModWithObjects</C>
in <Package>XMod</Package> works again.
This constructs a crossed module of groupoids with a connected range
and a homogeneous, discrete source.
<P/>
In recent versions there have been a number of changes of function
name, such as <C>IsDigraph</C> becoming <C>IsGroupoidDigraph</C>.
This is in order to avoid conflicts with the
<Package>Digraphs</Package> package.
<P/>
In version 1.62 of October 2018 there were significant changes to the
operations constructing free products with amalgamation and HNN extensions.
There was a plan to move this material to a new package
<Package>Rewriting</Package>, but that has not happened.
<P/>
Version 1.71 of August 2022 contains a complete revision of right,
left and double cosets of groupoids.
(The initial declaration of LeftCoset was moved to the
<Package>Utils</Package> package.)
<P/>
Version 1.73 of February 2023 contained a first attempt at an implementation
of double groupoids, as described in Chapter <Ref Chap='chap-double' />.
This was then extensively revised in version 1.77 of July 2025.
This experimental material is liable to be changed and extended.
A more general version of double groupoids has been introduced in the
<Package>XMod</Package> package.

</Section>

<Section Label="sec-whatnext">
<Heading>What needs to be done next?</Heading>

<List>
<Item>
more work on automorphism groups of groupoids;
</Item>
<Item>
normal subgroupoids and quotient groupoids;
</Item>
<Item>
more methods for morphisms of groupoids,
particularly when the range is not connected;
</Item>
<Item>
<C>ImageElm</C> and <C>ImagesSource</C>
for the cases of groupoid morphisms not yet covered;
</Item>
<Item>
<C>Enumerator</C> for <C>IsHomsetCosetsRep</C>;
</Item>
<Item>
free groupoid on a graph;
</Item>
<Item>
convert <C>GraphOfGroupsRewritingSystem</C> to the category
<C>IsRewritingSystem</C>;
</Item>
<Item>
in <Package>XMod</Package>, continue to work on crossed modules over groupoids;
</Item>
</List>

</Section>
</Chapter>

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