\begin{thebibliography}{1}

\bibitem{gee}
Jon Claerbout.
\newblock {\em Geophysical Estimation by Example}.
\newblock
  http://sepwww.\urlbr{}stanford.\urlbr{}edu/\urlbr{}sep/\urlbr{}prof/toc\_htm%
l/\urlbr{}toc\_html/\urlbr{}gee/\urlbr{}toc\_html/, 1999.

\bibitem{clapp1}
R.~Clapp, P.~Sava, and J.F. Claerbout.
\newblock Interval velocity estimation with a null space.
\newblock {\em Stanford Exploration Project Report,
  http://sepwww.\urlbr{}stanford.\urlbr{}edu/\urlbr{}research/\urlbr{}reports/%
}, 97:\mbox{147--156}, 1998.

\bibitem{dix}
C.~Hewett Dix.
\newblock {\em Seismic Prospecting for Oil}.
\newblock Harper and Brothers, 1952.

\bibitem{luenberger}
David~G. Luenberger.
\newblock {\em Introduction to Linear and Nonlinear Programming}.
\newblock Addison Wesley, 1973.

\bibitem{toldi85}
J.~L. Toldi.
\newblock {\em Velocity analysis without picking}.
\newblock PhD thesis, Stanford University, 1985.

\end{thebibliography}