added reference

--- a/doc-src/Codegen/Thy/Program.thy	Mon Jun 14 15:27:08 2010 +0200
+++ b/doc-src/Codegen/Thy/Program.thy	Mon Jun 14 15:27:09 2010 +0200
@@ -134,7 +134,8 @@
 
 text {*
   \noindent This is a convenient place to show how explicit dictionary construction
-  manifests in generated code (here, the same example in @{text SML}):
+  manifests in generated code (here, the same example in @{text SML})
+  \cite{Haftmann-Nipkow:2010:code}:
 *}
 
 text %quote {*@{code_stmts bexp (SML)}*}