template <typename T, class Container>
class Stack
{
protected:
  Container c_;

public:
  typedef T ValueType;
  // assumption: T and Container::ValueType are the same type

  void         Push  (const ValueType& t)  { c_.PushBack(t);    }
  void         Pop   ()                    { c_.PopBack();      }  // Precondition: !Empty() 
  ValueType&   Top   ()                    { return c_.Back();  }  // Precondition: !Empty()
  bool         Empty () const              { return c_.Empty(); }
  unsigned int Size  () const              { return c_.Size();  }
  void         Clear ()                    { c_.Clear();        }
} ;