src/HOL/Rat.thy

--- a/src/HOL/Rat.thy	Tue Apr 27 09:49:36 2010 +0200
+++ b/src/HOL/Rat.thy	Tue Apr 27 09:49:40 2010 +0200
@@ -440,7 +440,9 @@
 next
   fix q r :: rat
   show "q / r = q * inverse r" by (simp add: divide_rat_def)
-qed (simp add: rat_number_expand, simp add: rat_number_collapse)
+next
+  show "inverse 0 = (0::rat)" by (simp add: rat_number_expand, simp add: rat_number_collapse)
+qed
 
 end