\begin{thebibliography}{1}

\bibitem{Axe84BI}
O.~Axelsson, S.~Brinkkemper, and V.P. Il'in.
\newblock On some versions of incomplete block matrix factorization iterative
  methods.
\newblock {\em Lin. Algebra Appl. 59}, pages 3--15, 1984.

\bibitem{Con85GM}
P.~Concus, G.H. Golub, and G.~Meurant.
\newblock Block preconditioning for the conjugate gradient method.
\newblock {\em SIAM J. Sci. Stat. Comp. 6}, pages 220--252, 1985.

\bibitem{Kett_87}
Robert Kettler.
\newblock {\em Linear Multigrid Methods for Numerical Reservoir Simulation}.
\newblock University of Technology, Delft, december 1987.
\newblock Thesis.

\bibitem{Meu84}
G.~Meurant.
\newblock The block preconditioned conjugate gradient method on vector
  computers.
\newblock {\em BIT}, 24:623--633, 1984.

\end{thebibliography}
