src/HOL/Library/Library/document/root.bib

+
+ @Unpublished{Abrial-Laffitte,
+  author = 	 {Abrial and Laffitte},
+  title = 	 {Towards the Mechanization of the Proofs of
+                  Some Classical Theorems of Set Theory},
+  note = 	 {Unpublished}
+}
+
+@Book{Oberschelp:1993,
+  author =	 {Arnold Oberschelp},
+  title = 	 {Rekursionstheorie},
+  publisher = 	 {BI-Wissenschafts-Verlag},
+  year = 	 1993
+}
 
 @Book{davenport92,
   author =	 {H. Davenport},
   title = 	 {The Higher Arithmetic},
   publisher = 	 {Cambridge University Press},