Thanks Mr Stadnik. At end, I forgot the references. The “Introduction to Algorithms” is one of my favorite books. When I bought the book I had done my first implementation of the counter trees. I tried to use the balanced algorithms of the book in this version , but with counters of the nodes, was impossible, and I began from zero to design the algorithms based on the definition of Tree234. I will add references to the project. It can be useful for the people. About the double augmented tree for support accumulate function in a log (N) time, it is possible , but it is a hard work, because you must redesign all the algorithms for to balance the tree. In the countertree the insertion or deletion NOT invalidate the existing iterators. The iterator have a pointer to the node, and when you want to know the position, travel from their position to the root examining the node counters. If you insert an element in a previous position to one iterator, you can access to the element pointed by the iterator, but when you check the position you will obtain the next number. You can safely mix access, insertion and deletion with iterators and positions. You have arithmetic with the iterators, even with the end() and rend() iterators. unsigned D = V.end() - ( V.begin() +5) ; The arithmetic operations are log(N), because the iterators obtain the position as I described before. About the dynamically allocated augmented B+ trees, I must read more, in order to provide you a former opinion, but it looks very interested. About the Boost::container the data structures similar to the data structures of countertree, are implemented ( as I understand) over sorted vectors, or similar data structures, which have performance problems when insert or delete in central positions. But I must study more. Regards Francisco Tapia