[boost] [mpl]mpl::plus and non Integral Constants

Reading the mpl documentation it states that boost::mpl::plus is expected to be specialised for non Integral Constants. Therefore should the following work ?: typedef boost::mpl::plus<int,int>::type int_plus_int_type; // eg int presumably OTOH it could be said that: mpl::plus<int_<1>, int_<1> >::type and mpl::plus<int,int>::type are conceptually different and that therefore mpl::plus<int,int> should be(remain) invalid. Any thoughts? regards Andy Little