\begin{thebibliography}{1} \bibitem{kn:peano} Frederik Eriksen. \newblock Et bevis i peano aritmetik, 2005. \newblock Logiweb-dokument tilg\ae{}ngelig p\aa{} hjemmesiden: \url{http://www.diku.dk/~grue/logiweb/20050502/home/eriksen/peano-commutativ% ity/GRD-2005-06-29-UTC-11-26-23-740136}. \bibitem{kn:gold} Derek Goldrei. \newblock {\em Classic Set Theory --- For Guided Independent Study}. \newblock Chapman \& Hall, 1996. \bibitem{kn:base} Klaus Grue. \newblock A logiweb base page. \newblock Logiweb-dokument tilg\ae{}ngelig p\aa{} hjemmesiden: \url{http://www.diku.dk/~grue/logiweb/20060417/home/grue/base/GRD-2006-06-06% -UTC-07-18-19-012409}. \bibitem{kn:check} Klaus Grue. \newblock The logiweb sequent calculus. \newblock Logiweb-dokument tilg\ae{}ngelig p\aa{} hjemmesiden: \url{http://www.diku.dk/~grue/logiweb/20060417/home/grue/check/GRD-2006-06-0% 6-UTC-07-49-23-045248}. Dokumentet er fordelt p\aa{} tre .pdf-filer, hvis adresser (relativt til den ovenst\aa{}ende adresse) er: \href{http://www.diku.dk/~grue/logiweb/20060417/home/grue/check/GRD-2006-06-% 06-UTC-07-49-23-045248/body/tex/page.pdf}{body/tex/page.pdf}, \href{http://www.diku.dk/~grue/logiweb/20060417/home/grue/check/GRD-2006-06-% 06-UTC-07-49-23-045248/body/tex/appendix.pdf}{body/tex/appendix.pdf} og \href{http://www.diku.dk/~grue/logiweb/20060417/home/grue/check/GRD-2006-06-% 06-UTC-07-49-23-045248/body/tex/chores.pdf}{body/tex/chores.pdf}. De to f\o{}rste filer er s\aa{} langt de vigtigste. \bibitem{kn:hrba} Karel Hrbacek and Thomas Jech. \newblock {\em Introduction to Set Theory}. \newblock Marcel Dekker, third edition, 1999. \bibitem{kn:mendel} Elliott Mendelson. \newblock {\em Introduction to Mathematical Logic}. \newblock Chapman \& Hall, fourth edition, 1997. \end{thebibliography}