\begin{thebibliography}{Wielemaker \& Anjewierden, 1994}

\bibitem[Anjewierden, 1992]{XPCE:lisp}
A.~Anjewierden.
\newblock {\em {XPCE/Lisp}: {XPCE Common Lisp} Interface}.
\newblock {SWI}, University of Amsterdam, Roetersstraat 15, 1018 WB Amsterdam,
  The Netherlands, 1992.
\newblock E-mail: anjo@swi.psy.uva.nl.

\bibitem[Anjewierden {\em et al.}, 1990]{Anjewierden:90b}
A.~Anjewierden, J.~Wielemaker, and C.~Toussaint.
\newblock Shelley --- computer aided knowledge engineering.
\newblock In B.~Wielinga, J.~Boose, B.~Gaines, G.~Schreiber, and M.~van
  Someren, editors, {\em {Current trends in knowledge acquisition}}, pages 41
  -- 59, Amsterdam, May 1990. IOS Press.

\bibitem[Chambers {\em et al.}, 1989]{chambers:89}
Craig Chambers, David Ungar, and Elgin Lee.
\newblock An efficient implementation of {SELF}, a dynamic-typed
  object-oriented language based on prototypes.
\newblock {\em Sigplan Notices}, 24(10):49--70, Oct 1989.

\bibitem[Goldberg \& Robson, 1983]{Goldberg:83a}
A.~Goldberg and D.~Robson.
\newblock {\em {Smalltalk--80: The Language and its Implementation}}.
\newblock Addison-Wesley, 1983.

\bibitem[Wielemaker \& Anjewierden, 1989]{Wielemaker:89}
J.~Wielemaker and A.~Anjewierden.
\newblock {Separating User Interface and Functionality Using a Frame Based Data
  Model}.
\newblock In {\em Proceedings Second Annual Symposium on User Interface
  Software and Technology}, pages 25--33, Williamsburg, Virginia, November
  1989. ACM Press.

\bibitem[Wielemaker \& Anjewierden, 1993]{XPCE:reference}
J.~Wielemaker and A.~Anjewierden.
\newblock {\em {XPCE-4} Reference Manual}.
\newblock {SWI}, University of Amsterdam, Roetersstraat 15, 1018 WB Amsterdam,
  The Netherlands, 1993.
\newblock Paper version of online manual.

\bibitem[Wielemaker \& Anjewierden, 1994]{XPCE:cpp}
J.~Wielemaker and A.~Anjewierden.
\newblock {\em A {C++} interface for {XPCE}}.
\newblock {SWI}, University of Amsterdam, Roetersstraat 15, 1018 WB Amsterdam,
  The Netherlands, 1994.
\newblock E-mail: jan@swi.psy.uva.nl.

\bibitem[Wielemaker, 1992]{XPCE:draw}
J.~Wielemaker.
\newblock {\em {PceDraw}: An example of using {XPCE-4}}.
\newblock {SWI}, University of Amsterdam, Roetersstraat 15, 1018 WB Amsterdam,
  The Netherlands, 1992.
\newblock E-mail: jan@swi.psy.uva.nl.

\bibitem[Wielemaker, 1994]{XPCE:course}
J.~Wielemaker.
\newblock {\em {XPCE/Prolog} Course Notes}.
\newblock {SWI}, University of Amsterdam, Roetersstraat 15, 1018 WB Amsterdam,
  The Netherlands, 1994.
\newblock E-mail: jan@swi.psy.uva.nl.

\bibitem[Wielemaker, 1996]{SWI-Prolog:manual}
J.~Wielemaker.
\newblock {\em {SWI-Prolog 2.5}: Reference Manual}.
\newblock {SWI}, University of Amsterdam, Roetersstraat 15, 1018 WB Amsterdam,
  The Netherlands, 1996.
\newblock E-mail: jan@swi.psy.uva.nl.

\end{thebibliography}