text: const int XMAX=40;
  const int YMAX=24;
  
  struct point {
      int x,y;
      point() {}
      point(int a, int b) {x=a; y=b;}
  };
  
  extern void put_point(int a, int b);
  inline void put_point(point *p) { put_point(p->x,p->y); }
  
  extern void put_line(int, int, int, int);
  inline void put_line(point *a, point *b)
      { put_line(a->x,a->y,b->x,b->y); }
  
  extern void screen_init();
  extern void screen_destroy();
  extern void screen_refresh();
  extern void screen_clear();
  