diff --git a/Nef_3/include/CGAL/Nef_3/ID_support_handler.h b/Nef_3/include/CGAL/Nef_3/ID_support_handler.h
index 43e70d77d63..a6dd108b221 100644
--- a/Nef_3/include/CGAL/Nef_3/ID_support_handler.h
+++ b/Nef_3/include/CGAL/Nef_3/ID_support_handler.h
@@ -65,6 +65,16 @@ class ID_support_handler<SNC_indexed_items, Decorator> {
     hash.reserve(n);
   }
 
+  // The method get_hash implements a
+  // two-pass union find algorithm
+  //    __    __           _______
+  //   /  \  /  \         /  _____\
+  //  _|__|__|__|_      _/__/__/__|_
+  // | |  v  |  v |    | |  |  |  v |
+  // | O  O  O  O | => | O  O  O  O |
+  // |____|__^____|    |____________|
+  //      |  | root
+  //      \_/
   int get_hash(int i) {
     int root(i);
     while(hash[root] != root)