Fixed dependency on Dense_Linear_Order

--- a/src/HOL/MetisExamples/BigO.thy	Wed Feb 27 16:07:55 2008 +0100
+++ b/src/HOL/MetisExamples/BigO.thy	Wed Feb 27 16:41:36 2008 +0100
@@ -8,7 +8,7 @@
 header {* Big O notation *}
 
 theory BigO
-imports Main SetsAndFunctions 
+imports Dense_Linear_Order Main SetsAndFunctions 
 begin
 
 subsection {* Definitions *}