--- a/Nominal/ExLet.thy	Thu Apr 01 17:56:26 2010 +0200
+++ b/Nominal/ExLet.thy	Thu Apr 01 17:56:39 2010 +0200
@@ -92,6 +92,13 @@
   apply(simp_all add:permute_bn eqvts)
   done
 
+lemma fv_fv_bn:
+  "fv_bn l - set (bn l) = fv_lts l - set (bn l)"
+  apply(induct l rule: trm_lts.inducts(2))
+  apply(rule TrueI)
+  apply(simp_all add:permute_bn eqvts)
+  by blast
+
 lemma Lt_subst:
   "supp (Abs_lst (bn lts) trm) \<sharp>* q \<Longrightarrow> (Lt lts trm) = Lt (permute_bn q lts) (q \<bullet> trm)"
   apply (simp only: trm_lts.eq_iff)