class LispList<E> 
{
 private Cell<E> myList;

 private LispList(Cell<E> list)
 {
  myList=list;
 }

 public boolean isEmpty()
 {
  return myList==null;
 }

 public E head()
 {
  return myList.first;
 }

 public LispList<E> tail()
 {
  return new LispList<E>(myList.rest);
 }

 public LispList<E> cons(E item)
 {
  return new LispList<E>(new Cell<E>(item,myList));
 }

 public static <T> LispList<T> empty()
 {
  return new LispList<T>(null);
 }

 public boolean equals(Object other)
 {
  if(!(other instanceof LispList))
     return false;
  Cell<E> ptr1 = this.myList;
  Cell<E> ptr2 = ((LispList) other).myList;
  for(;ptr1!=ptr2&&ptr1!=null&&ptr2!=null; ptr1=ptr1.rest,ptr2=ptr2.rest)
     if(!ptr1.first.equals(ptr2.first))
        return false;
  return (ptr1==ptr2);
 }

 public String toString()
 {
  if(myList==null)
     return "[]";
  else
     return "["+myList.first+restToString(myList.rest);
 }

 private static <T> String restToString(Cell<T> l)
 {
  if(l==null)
     return "]";
  else
     return ","+l.first+restToString(l.rest);
 }

 private static class Cell <T>
 {
  T first;
  Cell<T> rest;

  Cell(T h,Cell<T> t)
  {
   first=h;
   rest=t;
  }
 }
 
}