\begin{thebibliography}{2}
\expandafter\ifx\csname natexlab\endcsname\relax\def\natexlab#1{#1}\fi
\expandafter\ifx\csname bibnamefont\endcsname\relax
  \def\bibnamefont#1{#1}\fi
\expandafter\ifx\csname bibfnamefont\endcsname\relax
  \def\bibfnamefont#1{#1}\fi
\expandafter\ifx\csname citenamefont\endcsname\relax
  \def\citenamefont#1{#1}\fi
\expandafter\ifx\csname url\endcsname\relax
  \def\url#1{\texttt{#1}}\fi
\expandafter\ifx\csname urlprefix\endcsname\relax\def\urlprefix{URL }\fi
\providecommand{\bibinfo}[2]{#2}
\providecommand{\eprint}[2][]{\url{#2}}

\bibitem[{car({\natexlab{a}})}]{carpet-carpetweb}
\emph{\bibinfo{title}{Mesh refinement with {Carpet}}},
  \urlprefix\url{http://www.carpetcode.org/}.

\bibitem[{car({\natexlab{b}})}]{carpet-cactusweb}
\emph{\bibinfo{title}{{Cactus} {Computational} {Toolkit}}},
  \urlprefix\url{http://www.cactuscode.org/}.

\end{thebibliography}
