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I hereby confirm that I prepared this thesis independently, by exclusive reliance on the literature and tools indicated therein.

This thesis has not been submitted to any other examination authoriy in its current or an altered form, and it has not been published.

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Osnabr{\"u}ck, June 1, 2007 
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\T\hspace*{19.5em} \scriptsize{\ (Emanuel Schütze)}
\W\newline Emanuel Sch{\"u}tze
