diff -r a331468b2f5a -r 7b5db6c23753 Nominal/Nominal2_Base.thy
--- a/Nominal/Nominal2_Base.thy	Thu May 31 10:05:19 2012 +0100
+++ b/Nominal/Nominal2_Base.thy	Thu May 31 11:59:56 2012 +0100
@@ -876,6 +876,10 @@
   shows "p \<bullet> (if b then x else y) = (if p \<bullet> b then p \<bullet> x else p \<bullet> y)"
   by (simp add: permute_fun_def permute_bool_def)
 
+lemma Let_eqvt [eqvt]:
+  shows "p \<bullet> Let x y = Let (p \<bullet> x) (p \<bullet> y)"
+  unfolding Let_def permute_fun_app_eq ..
+
 lemma True_eqvt [eqvt]:
   shows "p \<bullet> True = True"
   unfolding permute_bool_def ..