int main(void) {

  cons_cell *points;

  point p1 = {1,2}, p2 = {3,4}, 
        p3 = {5,6}, p4 = {6,7};

  points = cons(&p1,
                cons(&p2,
                     cons(&p3,
                          NULL)));

  set_head(points,&p3);
  set_head(tail(points), &p4);

  while (points != NULL) {
    prnt_point(*((point*)(head(points))));
    points = tail(points);
  }
  
  return 0;
}