# Simple bibliography error

I use this code and there is an error when I always refer to a webpage which contains _, and it says me missing \$ inserted. How could I cancel this problem?

\begin{thebibliography}{9}

\bibitem{Introduction to CFT}
Blumenhagen, R., Plauschinn, E., Introduction to Conformal Field Theory: With Applications
to String Theory, Lect. Notes Phys. 779 (Springer, Berlin Heidelberg 2009), DOI 10.1007
978-3-642-00450-6
\\\texttt{http://stringworld.ru/files/Blumenhagen_R._Plauschinn_E._Introduction_to_conformal_field_theory_with_applications_to_string_theory.pdf}

\end{thebibliography}

• _ should be \_ – David Carlisle Apr 26 '15 at 0:14

You shouldn't encase the URL in a \texttt directive. Instead, be sure to load the url package, possibly with the option hyphens, and then write \url{<long url string here>}.

\documentclass{article}

\usepackage{url}

\begin{document}
\begin{thebibliography}{9}

\bibitem{Introduction to CFT}
Blumenhagen, R., Plauschinn, E., Introduction to Conformal Field Theory:
With Applications to String Theory, Lect.\ Notes Phys.\ 779 (Springer,
Berlin and Heidelberg 2009), DOI 10.1007, ISBN 978-3-642-00450-6\linebreak
\url{http://stringworld.ru/files/Blumenhagen_R._Plauschinn_E._Introduction_to_conformal_field_theory_with_applications_to_string_theory.pdf}

\end{thebibliography}
\end{document}
`