class InsertList1
{
// A sequence type implemented using a doubly-linked list.

 private Cell ptr;

 public InsertList1()
 {
  ptr=null;
 }

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

 public boolean atEnd()
 {
  return ptr.next==null;
 }

 public boolean atStart()
 {
  return ptr.prev==null;
 }

 public void insert(Object obj)
 {
  if(ptr==null)
     ptr = new Cell(null,obj,null);
  else if(ptr.next==null)
     {
      ptr.next = new Cell(ptr,obj,null);
      ptr = ptr.next;
     }
  else
     {
      ptr.next.prev = new Cell(ptr,obj,ptr.next);
      ptr.next = ptr.next.prev;
      ptr=ptr.next;
     }
 }

 public void delete()
 {
  if(ptr.next==null)
     {
      ptr = ptr.prev;
      if(ptr!=null)
         ptr.next=null;
     }
  else
     {
      ptr.next.prev = ptr.prev;
      if(ptr.prev!=null)
         ptr.prev.next = ptr.next;
      ptr=ptr.next;
     }
 }

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

 public void backward()
 {
  ptr = ptr.prev;
 }

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

 private static class Cell
 {
  Cell prev,next;
  Object content;

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