Hi, boost::icl::interval_map<int, boost::icl::interval_map<int, boost::icl::interval_set<int>>> larger, smaller; larger.add(make_pair(boost::icl::discrete_interval<int>::closed(102,104), boost::icl::interval_map<int, boost::icl::interval_set<int>>{ make_pair(boost::icl::discrete_interval<int>::closed(0,0), boost::icl::interval_set<int>{boost::icl::discrete_interval<int>::closed(2,4)})})); smaller.add(make_pair(boost::icl::discrete_interval<int>::closed(103,103), boost::icl::interval_map<int, boost::icl::interval_set<int>>{ make_pair(boost::icl::discrete_interval<int>::closed(0,0), boost::icl::interval_set<int>{boost::icl::discrete_interval<int>::closed(3,3)})})); cout << larger << endl; cout << smaller << endl; cout << boost::icl::contains(larger, smaller) << endl; cout << ((smaller & larger) == smaller) << endl; As given above, I'm trying to check if smaller is subset of larger. But I get following output: {([102,104]->{([0,0]->{[2,4]})})} {([103,103]->{([0,0]->{[3,3]})})} 0 1 Any reason why boost::icl::contains(larger, smaller) doesn't work but ((smaller & larger) == smaller) works? Thanks.