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\newblock {\em A Logiweb base page}.
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\bibitem{grue:peano}
Klaus Grue.
\newblock {\em Peano arithmetic}.
\newblock http://www.diku.dk/\verb+~+grue/logiweb/
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\bibitem{mendelson}
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\newblock {\em Introduction to Mathematical Logic}.
\newblock Wadsworth and Brooks, 3. edition, 1987.

\end{thebibliography}
