diff -r ed9a1254d674 -r d3fca349736c src/HOL/Tools/datatype_abs_proofs.ML
--- a/src/HOL/Tools/datatype_abs_proofs.ML	Sat Sep 15 19:27:43 2007 +0200
+++ b/src/HOL/Tools/datatype_abs_proofs.ML	Sat Sep 15 19:27:44 2007 +0200
@@ -427,7 +427,7 @@
         val n = Sign.arity_number thy tyco;
       in
         thy
-        |> Class.prove_instance_arity (Class.intro_classes_tac [])
+        |> Class.prove_instance (Class.intro_classes_tac [])
             [(tyco, replicate n HOLogic.typeS, [HOLogic.class_size])] []
         |> snd
       end