Added "Executing higher order logic" paper.

--- a/doc-src/manual.bib	Mon Dec 31 14:08:23 2001 +0100
+++ b/doc-src/manual.bib	Mon Dec 31 14:13:07 2001 +0100
@@ -153,6 +153,16 @@
   author          = "Stefan Berghofer and Tobias Nipkow",
   pages           = "38--52"}
 
+@InProceedings{Berghofer-Nipkow:2002,
+  author =       {Stefan Berghofer and Tobias Nipkow},
+  title =        {Executing Higher Order Logic},
+  booktitle =    {Types for Proofs and Programs: TYPES'2000},
+  editor =       {P. Callaghan and Z. Luo and J. McKinna and R. Pollack},
+  series =       LNCS,
+  publisher =    Springer,
+  note =         {To appear},
+  year =         2002}
+
 @InProceedings{Berghofer-Wenzel:1999:TPHOL,
   author = 	 {Stefan Berghofer and Markus Wenzel},
   title = 	 {Inductive datatypes in {HOL} --- lessons learned in