Hello List, I would greatly appreciate if someone could assist me in getting this structure correct. boost::multi_index_container< std::list< std::pair< /*value*/ unsigned char, std::pair< /*x co-ordinate*/ unsigned char, /*y co-ordinate*/ unsigned char > > >, boost::multi_index::indexed_by< /*value*/ boost::multi_index::ordered_non_unique< boost::multi_index::identity<unsigned char> >, /*x co-ordinate*/ boost::multi_index::ordered_non_unique< boost::multi_index::identity<unsigned char> >, /*y co-ordinate*/ boost::multi_index::ordered_non_unique< boost::multi_index::identity<unsigned char> > > > m; I do not see how "boost::multi_index::ordered_non_unique" will index the appropriate field in the nested std::pair structures. This is why I suspect there to be a problem with this structure. So before I continue, could someone please tell me if I am on the correct path. Grateful, Etienne