--- a/doc-src/Ref/ref.bbl Wed Dec 01 12:45:49 1993 +0100
+++ b/doc-src/Ref/ref.bbl Wed Dec 01 12:48:47 1993 +0100
@@ -11,6 +11,12 @@
formula manipulation, with application to the {Church-Rosser Theorem}.
\newblock {\em Indagationes Mathematicae}, 34:381--392, 1972.
+\bibitem{nipkow-prehofer}
+Tobias Nipkow and Christian Prehofer.
+\newblock Type checking type classes.
+\newblock In {\em 20th ACM Symp.\ Principles of Programming Languages}, 1993.
+\newblock To appear.
+
\bibitem{paulson91}
Lawrence~C. Paulson.
\newblock {\em {ML} for the Working Programmer}.