boost::intrusive::list<Element, boost::intrusive::member_hook<Element, boost::intrusive::list_member_hook<>,
&Element::active_element_set_hook>>
active_element_set_;
boost::intrusive::list<Element, boost::intrusive::member_hook<Element, boost::intrusive::list_member_hook<>,
&Element::active_element_set_hook>>
active_element_set_;