When iterating though a bimap with a left iterator, I notice that for the pairs having the same left member e.g. (L, R1) (L,R2), (L,R3), ... the pairs are not in increasing R, but in the insertion order of the pairs. Is this an artefact of the design, or an intention? The actual bimap I am using is typedef boost::bimap< boost::bimaps::multiset_of< unsigned int >, boost::bimaps::multiset_of< unsigned int >, boost::bimaps::set_of_relation<>, boost::bimaps::with_info< int > > BMAP; I set it up so that info stores the insertion order index. Thanks.