namespace boost {
 template<typename R, typename T1, typename T2, ..., typename TN, 
 typename Combiner = last_value<R>, typename Group = int, 
 typename GroupCompare = std::less<Group>, 
 typename SlotFunction = functionN<R, T1, T2, ..., TN> > 
 class signalN;
 template<typename Signature, typename Combiner = last_value<R>, 
 typename Group = int, typename GroupCompare = std::less<Group>, 
 typename SlotFunction = functionN<Signature> > 
 class signal;
 namespace signals {

 enum connect_position { at_front, at_back };
 }
}

namespace boost {
 template<typename SlotFunction> class slot;
}

namespace boost {
 namespace signals {
 class trackable;
 }
}

namespace boost {
 namespace signals {
 class connection;
 void swap(connection&, connection&);
 class scoped_connection;
 }
}

namespace boost {
 template<typename Visitor, typename T> 
 void visit_each(const Visitor&, const T&, int);
}

namespace boost {
 template<typename T> class last_value;

 template<> class last_value<void>;
}