\begin{thebibliography}{9}
\bibitem{S}
Richard A. Becker, John M. Chambers, and Allan R. Wilks (1988)
{\em The New S Language},
Wadsworth, Pacific Grove, California.
\bibitem{Clos}
Sonya E. Keene (1989)
{\em Object-Oriented Programming in COMMON LISP:
A Programmer's Guide to CLOS},
Addison-Wesley, Reading, Massachusetts.
\bibitem{CPP}
Bjarne Stroustrup (1986)
{\em The C++ Programming Language},
Addison-Wesley, Reading, Massachusetts.

\end{thebibliography}
