diff -r 7fcc0179fb21 -r 134639e6ea45 lemon/elevator.h
--- a/lemon/elevator.h	Mon Feb 19 19:55:13 2007 +0000
+++ b/lemon/elevator.h	Tue Feb 20 12:55:37 2007 +0000
@@ -146,6 +146,9 @@
     }
   
     ///Activate item \c i.
+
+    ///Activate item \c i.
+    ///\pre Item \c i shouldn't be active before.
     void activate(Item i)
     {
       const int l=_level[i];
@@ -154,6 +157,9 @@
     }
   
     ///Deactivate item \c i.
+
+    ///Deactivate item \c i.
+    ///\pre Item \c i must be active before.
     void deactivate(Item i)  
     {
       swap(_where[i],_last_active[_level[i]]--);