namespace boost {
  namespace itl {
    template<class Type > class property;
    template<class Type > class member_property;
    template<class Type > class empty;

    template<class Type > struct is_neutron;

    template<class Type > class content_is_neutron;
    template<class LeftT , class RightT > class relation;

    template<class Type > struct std_equal;
    template<class Type > struct element_equal;
    template<class Type > struct protonic_equal;
    template<class Type > struct sub_super_set;
    template<class Type > struct super_sub_set;
  }
}