# Bibliography doesnt work -> missing item

My bibliography of my tex document doesnt work and i cant find out why. I created 2 books in bibTex, but if I refer to them via

 %%% Main Document
\bibliography{Seminar}
\begin{thebibliography}
\bibitem[Knuth98]{ComProgram} \emph{The Art of Computer Programming}
\end{thebibliography}


the compiler says missing item on these lines. I did it just as in the tutorial in wich i found these lines. The bib file is also in the same folder as the document. I found many tutorials on google but i just dont seem to get it.

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The problem is the missing argument to thebibliography, which specifies the widest label:
\begin{thebibliography}{Knuth98}

Note. If you are using directly the thebibliography environment, the \bibliography command is useless.