--- a/LMCS-Paper/document/root.bib	Sun Sep 18 22:52:56 2011 +0200
+++ b/LMCS-Paper/document/root.bib	Mon Sep 19 21:52:59 2011 +0200
@@ -1,3 +1,16 @@
+@inproceedings{pfenningsystem,
+  author =       "Frank Pfenning and Carsten Sch{\"u}rmann", 
+  title =        "System Description: Twelf---{A} Meta-Logical
+                  Framework for Deductive Systems",
+  booktitle =    "Automated Deduction",
+  series =       "LNAI",
+  volume =       1632,
+  pages =        "202--206",
+  year =         1999
+}
+
+
+
 @Article{ Urban08,
 	author = "C. Urban",
 	title = "{N}ominal {T}echniques in {I}sabelle/{HOL}",