\begin{thebibliography}{1}

\bibitem{Num-Sol}
K.E. Brenan, S.L. Campbel, and L.R. Petzold.
\newblock {\em Numerical Solution of Initial-Value Problems in
  Differential-Algebraic Equations}.
\newblock Elevier Science, 1989.

\end{thebibliography}
