C++ compiler unable to find function (namespace related)

(MAIN-NAMESPACE){

      a bunch of functions/classes I need to implement...

      (EXCEPTIONS-NAMESPACE){

            a bunch of exceptions
      }

      (POINTER-COLLECTIONS-NAMESPACE){

            Set and LinkedList classes, plus iterators
      }
}

template<typename T>
std::ostream& operator<<(std::ostream& os,
                         const MAIN-NAMESPACE::POINTER-COLLECTIONS-NAMESPACE::Set<T>& set)

Set A
Set B
Set C
double num

namespace A
{
namespace B
{
  class C{};
}

}

void f(A::B::C*);

namespace A
{
  void f(int*); // try commenting
  using ::f; // these two lines
  void g()
  {
    B::C* c;
    f(c);
  }
}

::operator<<( cout, myObj );

namespace MTM {//This is the MAIN-NAMESPACE

    namespace PointerCollections {

        (ITERATORS AND PREDICATE CLASSES)

        template<typename T>
        class Set {
        public:

        /////////////////////////////////
        // Definitions
        /////////////////////////////////

        private:

        /////////////////////////////////
        // Definitions
        /////////////////////////////////

        };


///////////////////////////////////////////////////////////////////////////////
// The implementation part.
///////////////////////////////////////////////////////////////////////////////
      }
}
// operator<< - the same a Set::print(std::ostream& os,
//                                    const BinaryPredicate<T>& predicate)
// function called with the 'predicate' parameter omitted
template<typename T>
std::ostream& operator<<(std::ostream& os,
                         const MTM::PointerCollections::Set<T>& set){

    set.print(os);
    return os;
}

namespace MTM {
    using std::ostream;

    class Schedule {
    public:
      ///////////////////
      //Definitions, including:
      ///////////////////
    void registerStation(string stationName);
    void reportRegisteredStations(std::ostream& outputStream) const;

    private:     //My database
               //All the classes Set recieves are defined elsewhere
    	Set<RegisteredStation> places;
    	Set<BusLine> busses;
    	Set<TrainLine> trains;
    	double tarifForBuses;
    	double tarifForTrains;
    };

}

Schedule s();
s.registerStation("1");
s.reportRegisteredStations(cout);//This invokes the error. Definition follows:

void Schedule::reportRegisteredStations(std::ostream& outputStream) const{

    	outputStream<<places;
    }

#include <iostream>
#include <string>
using std::string;

   namespace MTM {//This is the MAIN-NAMESPACE

    namespace PointerCollections {

        template<typename T>
        class Set {
        };


      }
}
template<typename T>
std::ostream& operator<<(std::ostream& os,
                         const MTM::PointerCollections::Set<T>& set){

    return os;
}

namespace MTM {
    using std::ostream;
  using PointerCollections::Set;
    class Schedule {
    public:
      ///////////////////
      //Definitions, including:
      ///////////////////
    void registerStation(string stationName);
    void reportRegisteredStations(std::ostream& outputStream) const;

    private:     //My database
               //All the classes Set recieves are defined elsewhere
        Set<int> places;
        Set<int> busses;
        Set<int> trains;
        double tarifForBuses;
        double tarifForTrains;
    };
void Schedule::reportRegisteredStations(std::ostream& outputStream) const{

        outputStream<<places;
    }

}

int main()
{
  MTM::Schedule s;
  s.reportRegisteredStations(std::cout);
}

namespace test {
    class A {};
}

namespace test {
    std::ostream& operator<<( std::ostream&, A const & );
}

namespace test2 {
   void g() {
      namespace1::class1 c1;
      namespace2::namespace3::class2 c2;
      f( c1, c2 );
   }
}