Hi this message is to announce the new version of the countertree library. According with the sugest of Rene Rivera ( Thanks), I had changed the namespaceof the library. Now all is in the namespace cntree. And in the documentation I have a big title with the text preliminary in the head of all the pages. If something is not OK , please mail me , and I will change as soon as possible. You can find the zip file with the code and the documentation in < http://www.boost-consulting.com/vault/index.php?action=downloadfile&filename=countertree.zip&directory=Containers&> or if you want a quick look , you can see in my web page < http://fjtapia.webs.com/works/countertree/index.html> The counter trees are trees where each node have an additional counter. This counter represent the number of nodes under it, including itself. This permit to access to the elements of the tree by their position, like a vector. You can mix safely access by iterators and access by position. This Library provide us : 1.- Vectors with the same speed inserting and deleting in the extreme positions than in the central positions. They are a bit slower than the STL vector inserting and deleting in the extreme positions, but much more faster inserting and deleting in the central positions. 2.- Set, multiset, map, multimap fully compatible with the STL set, multiset, map and multimap, with similar speed.The iterators are, like in a vector, random access (you can add or subtract any integer value to an iterator). You have too access to the elements by position like in a vector, with the function at (position) as you can see in the next example code #include <boost/countertree/set.hpp> #include <iostream> int main ( void ) { //------------------------ begin -------------------- cntree::set<int> A ; for ( int i = 0 ; i< 100 ; ++i) A.insert(i); for ( int i = 0 ; i < A.size() ; ++i) std::cout<<A.at(i); return 0 ; }; The iterators and the data structures are fully compatible with the STL functions and algorithms. For to show the utility of this, imagine a large unordered file with the information about the employees of a big company. You have indexes implemented with multimaps, with pairs [value, position], and use the upper_bound and lower_bound functions . You need to select the employees in a range of age and weight. With the boost:multimap you can know the number of elements of the selection. In the weight query we found 100 elements and in the age query 10000 elements. To travel the elements of the weight query asking for the age, is faster than the opposite. Tray it. It fast, useful and easy to understand and use,. They are the STL classes with a few additional functions. I had checked this code with GCC (32 and 64) and Visual Studio 2008 (32) and Visual Studio 1010 (32 and 64). Please, if you find any problem, please mail me ( <fjtapia@gmail.com>) or if you mail Boost, please insert [countertree] in the head of the message. Some days I have not time to read all messages arrived to my mail, but if I see that I detect and respond quickly. Francisco Tapia <fjtapia@gmail.com>