GAP (groupoids) - Chapter 8: Development History

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8 Development History
8.1 Versions of the Package
8.2 What needs to be done next?

### 8 Development History

#### 8.1 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 when the website at Bangor changed.

Since then, the package has been rewritten again, introducing magmas with objects and their mappings. Functions to implement constructions contained in [AW10] have been added, but this is ongoing work.

Versions 1.09 to 1.15 were prepared for the anticipated release of GAP 4.5 in June 2012.

Gpd became an accepted GAP package in May 2015.

In April 2017 the package was renamed again, as groupoids.

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.

In September 2017 various functions were revised so that, at last, the operation `DiscreteNormalPreXModWithObjects` in XMod works again. This constructs a crossed module of groupoids with a connected range and a homogeneous, discrete source.

In recent versions there have been a number of changes of function name, such as `IsDigraph` becoming `IsGroupoidDigraph`. This is in order to avoid conflicts with the Digraphs package. The intention is that these functions can revert to the original names in due course.

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 Rewriting, but that has not happened.

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 Utils package.)

#### 8.2 What needs to be done next?

- more work on automorphism groups of groupoids;

- 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;

- convert `GraphOfGroupsRewritingSystem` to the category `IsRewritingSystem`;

- in XMod, continue to work on crossed modules over groupoids.

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