Please use one of the following samples to cite GAP version from this installation

Text:

[GAP]  GAP  –  Groups,  Algorithms,  and Programming, Version 4.dev, 
The GAP Group (this year), https://www.gap-system.org.

HTML:

<p class='BibEntry'>
[<span class='BibKey'>GAP</span>]   
 <i class='BibTitle'>GAP – Groups, Algorithms, and Programming, Version 4.dev</i>,
 <span class='BibOrganization'>The GAP Group</span> (<span class='BibYear'>this year</span>),
<span class='BibHowpublished'><a href="https://www.gap-system.org">https://www.gap-system.org</a></span>.
</p>

BibXML:

<entry id="GAP4.dev"><misc>
  <title><C>GAP</C> &ndash; <C>G</C>roups, <C>A</C>lgorithms,
         and <C>P</C>rogramming, <C>V</C>ersion 4.dev</title>
  <howpublished><URL>https://www.gap-system.org</URL></howpublished>
  <year>this year</year>
  <key>GAP</key>
  <keywords>groups; *; gap; manual</keywords>
  <other type="organization">The GAP <C>G</C>roup</other>
</misc></entry>

BibTeX:

@misc{ GAP4.dev,
  title =            {{GAP} {\textendash} {G}roups, {A}lgorithms, and {P}rogramming, {V}ersion 4.dev},
  organization =     {The GAP {G}roup},
  year =             {this year},
  howpublished =     {\href{https://www.gap-system.org}{\texttt{https://www.gap-system.org}}},
  key =              {GAP},
  keywords =         {groups; *; gap; manual}
}

If you are not using BibTeX, here is the bibliography entry produced 
by BibTeX (in bibliography style `alpha'):

\bibitem[GAP]{GAP4}
\emph{GAP -- Groups, Algorithms, and Programming}, Version 4.dev,
The GAP~Group (this year), \verb+https://www.gap-system.org+.

If you have (predominantly) used one or more particular GAP packages,
please cite these packages in addition to GAP itself (either check the
the package documentation for the suggestions, or use a scheme like:

[PKG]
<Author name(s)>, <package name>, <package long title>, 
Version <package version> (<package date>), (GAP package),
<package URL>.

You may also produce citation samples for a GAP package by entering

    Cite("packagename");

in a GAP installation with the working version of this package available.