diff -r 091abf849a26 -r ef782bbf2d09 src/HOL/IntDiv.thy
--- a/src/HOL/IntDiv.thy	Tue Jul 24 19:46:44 2007 +0200
+++ b/src/HOL/IntDiv.thy	Tue Jul 24 19:58:53 2007 +0200
@@ -1231,6 +1231,11 @@
   thus ?thesis by blast
 qed
 
+lemma zdvd_zmult_cancel_disj[simp]:
+  "(k*m) dvd (k*n) = (k=0 | m dvd (n::int))"
+by (auto simp: zdvd_zmult_mono dest: zdvd_mult_cancel)
+
+
 theorem ex_nat: "(\<exists>x::nat. P x) = (\<exists>x::int. 0 <= x \<and> P (nat x))"
   apply (simp split add: split_nat)
   apply (rule iffI)