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src/HOL/Algebra/Ring.thy
changeset 23957 54fab60ddc97
parent 23350 50c5b0912a0c
child 26202 51f8a696cd8d 
--- a/src/HOL/Algebra/Ring.thy	Tue Jul 24 15:21:54 2007 +0200
+++ b/src/HOL/Algebra/Ring.thy	Tue Jul 24 15:29:57 2007 +0200
@@ -471,8 +471,8 @@
   with R show ?thesis by (simp add: a_assoc r_neg )
 qed
 
-lemma (in ring) minus_eq:
-  "[| x \<in> carrier R; y \<in> carrier R |] ==> x \<ominus> y = x \<oplus> \<ominus> y"
+lemma (in abelian_group) minus_eq:
+  "[| x \<in> carrier G; y \<in> carrier G |] ==> x \<ominus> y = x \<oplus> \<ominus> y"
   by (simp only: a_minus_def)
 
 text {* Setup algebra method:
isabelle