Michael B. Cherkassoff wrote in his e-mail message of 1994/03/07

Can anybody advise me how to cite GAP in the paper.

The best answer would be database entry for LaTex.

Citing the manual is the right way to go. Here is an entry.

[S+ 93] Martin Sch"onert et.al. GAP -- Groups, Algorithms, and Programming.
Lehrstuhl D f"ur Mathematik, Rheinisch Westf"alische Technische
Hochschule, Aachen, Germany, third edition, 1993.

So a BibTeX entry for a quotation of the GAP manual should read:

@string{ RWTH      = "Rheinisch Westf{\accent127 a}lische Technische
                      Hoch\-schule"                                     }
@string{ RWTHLDFM  = "Lehrstuhl D f{\accent127 u}r Mathematik,
                      Rheinisch Westf{\accent127 a}lische Technische
                      Hoch\-schule"                                     }
@string{ RWTH-A    = "Aachen, Germany"                                  }

@manual{Sch93,
author        = "Martin Sch{\accent127 o}nert and others",
title         = "{GAP} -- {Groups}, {Algorithms}, and {Programming}",
year          = "1993",
edition       = "third",
organization  = RWTHLDFM,
address       = RWTH-A,
notes         = "PAGES: 900",
keywords      = "groups; *; gap; manual"
}

If you are not using BibTeX, here is the bibliography entry produced by
BibTeX. You can use this inside the bibliography environment of LaTeX.

\newcommand{\etalchar}[1]{$^{#1}$}

\bibitem[S{\etalchar{+}}93]{Sch93}
          Martin Sch{\accent127 o}nert et~al.
\newblock {\em {GAP} -- {Groups}, {Algorithms}, and {Programming}}.
\newblock Lehrstuhl D f{\accent127 u}r Mathematik,
          Rheinisch Westf{\accent127 a}lische Technische Hoch\-schule,
          Aachen, Germany, third edition, 1993.

Martin.

-- .- .-. - .. -.  .-.. --- ...- . ...  .- -. -. .. -.- .-
Martin Sch"onert,   Martin.Schoenert@Math.RWTH-Aachen.DE,   +49 241 804551
Lehrstuhl D f"ur Mathematik, Templergraben 64, RWTH, 52056 Aachen, Germany