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# 2.4 Historical Remarks and Acknowledgements

A first program for drawing a diagram showing the lattice of subgroups of a finite group that had been calculated by a computer was implemented by H. Jürgensen in 1965 (see FJ65).

The design of XGAP was strongly influenced and in fact triggered by the QUOTPIC system of Derek Holt and Sarah Rees (see HR91) which allows to depict graphically knowledge about normal subgroups of a finitely presented group found by a variety of methods for the investigation of finitely presented groups. It seemed most desirable to allow to depict in a similar way the even wider variety of information on subgroups of groups that can be obtained by a system such as GAP.

Beginning 1993, Frank Celler developed the idea of an interface from GAP to graphic systems that allowed to actually write commands for graphical tasks in the GAP language and together with Susanne Keitemeier (see SK95) wrote a first version of programs in XGAP for drawing diagrams representing posets of subgroups of finite and finitely presented groups. We most gratefully acknowledge the help of Sarah Rees in implementing the interactive lattice functions and in beta testing the GAP3 version of XGAP.

In 1998, Thomas Breuer, Frank Celler, Joachim Neubüser and Max Neunhöffer planned the new concepts for the GAP4 version. The implementation and portation to GAP4 was done mainly by Max Neunhöffer in 1998 and 1999. Michael Ringe added the link to his MeatAxe programs. We like to thank all those who have adapted the GAP library to the needs of the new XGAP, in particular Alexander Hulpke who has been extremely helpful with this task.

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