diff --git a/src/backend/lib/dllist.c b/src/backend/lib/dllist.c
index b771fce..79c402e 100644
*** a/src/backend/lib/dllist.c
--- b/src/backend/lib/dllist.c
***************
*** 212,214 ****
--- 212,336 ----
  	l->dll_head = e;
  	/* We need not check dll_tail, since there must have been > 1 entry */
  }
+ 
+ /* Insert a node after the given target node. */
+ void
+ DLAddAfter(Dlelem *e, Dlelem *target)
+ {
+ 	Dllist	*l = target->dle_list;
+ 
+ 	e->dle_list = l;
+ 	e->dle_prev = target;
+ 	e->dle_next = target->dle_next;
+ 
+ 	if (l->dll_tail != target)
+ 	{
+ 		/* Target is not the tail */
+ 		Assert(target->dle_next != NULL);
+ 		target->dle_next->dle_prev = e;
+ 	}
+ 	else
+ 	{
+ 		/* Target is the tail */
+ 		Assert(target->dle_next == NULL);
+ 		l->dll_tail = e;
+ 	}
+ 	target->dle_next = e;
+ 	return;
+ }
+ 
+ /* Insert a node before the given target node. */
+ void
+ DLAddBefore(Dlelem *e, Dlelem *target)
+ {
+ 	Dllist	*l = target->dle_list;
+ 
+ 	e->dle_list = l;
+ 	e->dle_prev = target->dle_prev;
+ 	e->dle_next = target;
+ 
+ 	if (l->dll_head != target)
+ 	{
+ 		/* Target is not the head */
+ 		Assert(target->dle_prev != NULL);
+ 		target->dle_prev->dle_next = e;
+ 	}
+ 	else
+ 	{
+ 		/* Target is the head */
+ 		Assert(target->dle_prev == NULL);
+ 		l->dll_head = e;
+ 	}
+ 	target->dle_prev = e;
+ 	return;
+ }
+ 
+ /* Swap a node with its successor */
+ void
+ DLSwapWithNext(Dlelem *e)
+ {
+ 	Dllist	*l = e->dle_list;
+ 	Dlelem	*tmp;
+ 
+ 	Assert(e->dle_next != NULL);
+ 
+ 	tmp = e->dle_next;
+ 	e->dle_next = tmp->dle_next;
+ 	if (l->dll_tail != tmp)
+ 	{
+ 		Assert(tmp->dle_next != NULL);
+ 		tmp->dle_next->dle_prev = e;
+ 	}
+ 	else
+ 	{
+ 		l->dll_tail = e;
+ 	}
+ 	if (l->dll_head != e)
+ 	{
+ 		Assert(e->dle_prev != NULL);
+ 		e->dle_prev->dle_next = tmp;
+ 	}
+ 	else
+ 	{
+ 		l->dll_head = tmp;
+ 	}
+ 	tmp->dle_prev = e->dle_prev;
+ 	e->dle_prev = tmp;
+ 	tmp->dle_next = e;
+ 	return;
+ }
+ 
+ /* Swap a node with its predecessor */
+ void
+ DLSwapWithPrevious(Dlelem *e)
+ {
+ 	Dllist	*l = e->dle_list;
+ 	Dlelem	*tmp;
+ 
+ 	Assert(e->dle_prev != NULL);
+ 
+ 	tmp = e->dle_prev;
+ 	e->dle_prev = tmp->dle_prev;
+ 	if (l->dll_head != tmp)
+ 	{
+ 		Assert(tmp->dle_prev != NULL);
+ 		tmp->dle_prev->dle_next = e;
+ 	}
+ 	else
+ 	{
+ 		l->dll_head = e;
+ 	}
+ 	if (l->dll_tail != e)
+ 	{
+ 		Assert(e->dle_next != NULL);
+ 		e->dle_next->dle_prev = tmp;
+ 	}
+ 	else
+ 	{
+ 		l->dll_tail = tmp;
+ 	}
+ 	tmp->dle_next = e->dle_next;
+ 	e->dle_next = tmp;
+ 	tmp->dle_prev = e;
+ 	return;
+ }
diff --git a/src/include/lib/dllist.h b/src/include/lib/dllist.h
index d754b03..597e71f 100644
*** a/src/include/lib/dllist.h
--- b/src/include/lib/dllist.h
***************
*** 72,77 ****
--- 72,81 ----
  extern Dlelem *DLRemHead(Dllist *list); /* remove and return the head */
  extern Dlelem *DLRemTail(Dllist *list);
  extern void DLMoveToFront(Dlelem *e);	/* move node to front of its list */
+ extern void DLAddAfter(Dlelem *e, Dlelem *target); /* add node after another */
+ extern void DLAddBefore(Dlelem *e, Dlelem *target); /* same, but add before */
+ extern void DLSwapWithNext(Dlelem *e);
+ extern void DLSwapWithPrevious(Dlelem *e);
  
  /* These are macros for speed */
  #define DLGetHead(list)  ((list)->dll_head)