diff --git a/iter-seg-tree/include/iter_seg_tree.hpp b/iter-seg-tree/include/iter_seg_tree.hpp
index 639abf5..c3b35ad 100644
--- a/iter-seg-tree/include/iter_seg_tree.hpp
+++ b/iter-seg-tree/include/iter_seg_tree.hpp
@@ -64,6 +64,7 @@ class IterSegTree {
                 result = combine_(result, seg_tree_[--right]);
         }
 
+        // NOTE: if you separate, MUST combine at the end
         return result;
     }
 };
\ No newline at end of file