instances comm_semiring_0_cancel < comm_semiring_0, comm_ring < comm_semiring_0_cancel

--- a/src/HOL/Ring_and_Field.thy	Thu Sep 04 21:12:06 2008 +0200
+++ b/src/HOL/Ring_and_Field.thy	Fri Sep 05 00:19:50 2008 +0200
@@ -89,6 +89,8 @@
 
 subclass semiring_0_cancel ..
 
+subclass comm_semiring_0 ..
+
 end
 
 class zero_neq_one = zero + one +
@@ -282,7 +284,7 @@
 begin
 
 subclass ring ..
-subclass comm_semiring_0 ..
+subclass comm_semiring_0_cancel ..
 
 end