added lemma

--- a/src/HOL/IMP/Abs_Int2_ivl.thy	Thu May 02 21:04:50 2013 +0200
+++ b/src/HOL/IMP/Abs_Int2_ivl.thy	Fri May 03 02:52:25 2013 +0200
@@ -186,6 +186,9 @@
 lemma inf_ivl_nice: "[l1\<dots>h1] \<sqinter> [l2\<dots>h2] = [max l1 l2\<dots>min h1 h2]"
 by transfer (simp add: inf_rep_def)
 
+lemma top_ivl_nice: "\<top> = [-\<infinity>\<dots>\<infinity>]"
+by (simp add: top_ivl_def)
+
 
 instantiation ivl :: plus
 begin