\begin{thebibliography}{EGN}

\bibitem[EGN]{cryst}
Bettina Eick, Franz Gahler, and Werner Nickel.
\newblock cryst.
\newblock {https://www.gap-system.org/Packages/cryst.html}.

\bibitem[Ell]{hap}
Graham Ellis.
\newblock Hap.
\newblock {http://hamilton.nuigalway.ie/Hap/www/}.

\end{thebibliography}
