Added month for Coens thesis

--- a/doc-src/Logics/logics.bbl	Fri Nov 11 10:53:41 1994 +0100
+++ b/doc-src/Logics/logics.bbl	Mon Nov 14 10:41:25 1994 +0100
@@ -39,7 +39,7 @@
 \bibitem{coen92}
 Martin~D. Coen.
 \newblock {\em Interactive Program Derivation}.
-\newblock PhD thesis, University of Cambridge, 1992.
+\newblock PhD thesis, University of Cambridge, November 1992.
 \newblock Computer Laboratory Technical Report 272.
 
 \bibitem{constable86}