#ifndef Booster_#define Booster_template <class T> class BinaryTreeNode;class Booster {    friend void main(void);    friend void PlaceBoosters(BinaryTreeNode<Booster> *);   public:      void Output(ostream& out) const      {out << boost << ' ' << D << ' ' << d << ' ';}//   private: g++ has a problem when main is a friend      int D,       // degradation to leaf          d;       // degradation from parent      bool boost;  // true iff booster here};// overload <<ostream& operator<<(ostream& out, Booster x)   {x.Output(out); return out;}#endif