--- a/thys/Exercises.thy	Tue Jul 18 18:39:20 2017 +0100
+++ b/thys/Exercises.thy	Wed Jul 19 14:55:46 2017 +0100
@@ -1,5 +1,5 @@
 theory Exercises
-  imports Lexer "~~/src/HOL/Library/Infinite_Set"
+  imports Spec "~~/src/HOL/Library/Infinite_Set"
 begin
 
 section {* Some Fun Facts *}