I can't understand why derefencing begin of set<int,char> gives set2<int,char>, not char or int as one would expect. typedef set<int,char> s; typedef deref<begin<s>::type>::type e; BOOST_MPL_ASSERT(( or_<is_same<e,int>, is_same<e,char> > )); If I change s definition to typedef insert<set<int>,char>::type s; it compiles fine on gcc 3.4 and intel-linux 8.0. -- Alexander Nasonov