Vielleicht macht das Sinn:

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\usepackage{graphicx}
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\usepackage{sectsty}
\usepackage{appendix}
\usepackage{framed}
\usepackage{natbib}
\usepackage{url}
\usepackage{textcomp}
\usepackage{setspace}
\usepackage{scrpage2} % paket f{\"u}r kopf- und fu{\ss}zeilen
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\frontmatter

\include{chapters/title}
\tableofcontents
\listoffigures
\listoftables
\include{chapters/abbrev}

\mainmatter

\include{chapters/introduction}
\include{chapters/chap2}
\include{chapters/chap3}
\include{chapters/chap4}
\include{chapters/conclusion}

\bibliographystyle{gerapali}
\bibliography{literature/bibliography}

\addcontentsline{toc}{chapter}{Appendix}
\appendix
\include{chapters/appendix}

\include{erklaerung}

\end{document}