#include <iostream>
using namespace std;


class Receiver
{

  public:
    void open()
    {
      cout<<"Document is open" ;
    }

    void save()
    {
      cout<<"Document is saved" ;
    }

};

class command
{
   public:
   virtual void execute() =0;
};

class open : public command
{

   Receiver *recv;

   public: 

   open(Receiver *rec):recv(rec){}
   
     void execute()
     {
         recv.open();
     }

};

class save : public command
{
    Receiver *recv;

   public: 

   open(Receiver *rec):recv(rec){}

     void execute()
     {
         recv.save();
     }
 
};


class invoker
{
    list<command*> comm;

    public:
    void addcommand()
    {
        
    }

   void removecommand()
   {
    
   }

    void invoke command()
    {
    
    }


};

int main() {
    std::cout << "Hello world!" << std::endl;
    return 0;
}