void pre_combine (std::vector<boost::shared_ptr<Region> >&);
void post_combine (std::vector<boost::shared_ptr<Region> >&, boost::shared_ptr<Region>);
void pre_uncombine (std::vector<boost::shared_ptr<Region> >&, boost::shared_ptr<Region>);
void pre_combine (std::vector<boost::shared_ptr<Region> >&);
void post_combine (std::vector<boost::shared_ptr<Region> >&, boost::shared_ptr<Region>);
void pre_uncombine (std::vector<boost::shared_ptr<Region> >&, boost::shared_ptr<Region>);