class InsertList2
{
// A sequence type implemented using two singly-linked lists.

 private Cell before,after;

 public InsertList2()
 {
  before=null;
  after=null;
 }

 public boolean isEmpty()
 {
  return before==null&&after==null;
 }

 public boolean atEnd()
 {
  return after==null;
 }

 public boolean atStart()
 {
  return before.next==null;
 }

 public void insert(Object obj)
 {
  before = new Cell(obj,before);
 }

 public void delete()
 {
  before = before.next;
 }

 public void forward()
 {
  Cell ptr=after;
  after=after.next;
  ptr.next=before;
  before=ptr;
 }

 public void backward()
 {
  Cell ptr=before;
  before=before.next;
  ptr.next=after;
  after=ptr;
 }

 public Object current()
 {
  return before.content;
 }
 
 public String toString()
 {
  Cell ptr;
  String str="";
  if(before==null)
     return "";
  for(ptr=before.next; ptr!=null; ptr=ptr.next)
     str="  "+ptr.content+"\n"+str;
  str=str+"> "+before.content+"\n";
  for(ptr=after; ptr!=null; ptr=ptr.next)
     str=str+"  "+ptr.content+"\n";
  return str;
 }

 private static class Cell
 {
  Cell next;
  Object content;

  Cell(Object obj,Cell n)
  {
   content=obj;
   next=n;
  }
 }
}