I noticed that array.hpp uses #ifndef BOOST_ARRAY_HPP #define BOOST_ARRAY_HPP .. #endif and array_traits.hpp uses: #if !defined(BOOST_ARRAY_HPP) #define BOOST_ARRAY_HPP 1 .. #endif This means that you cant use them both at the same time? The first one wins? These are certainly similar classes but they dont seem to collide. Is this a subtle bug or intentional? ..Duane