generic 
  type ITEM_TYPE is private;
  with function ">="(L,R: ITEM_TYPE) return BOOLEAN is <>;
  with function "<"(L,R: ITEM_TYPE) return BOOLEAN is <>;
package RINGS is
-- All these priority queue implementations assume that the priority (i.e.,
-- the ordering relationships) of an item will not change once it is in the
-- queue.  That is, for correct operation, changing the priority of an item
-- requires:

-- 1. delete it from queue;
-- 2. change the priority;
-- 3. reinsert it in the queue.
  type QUEUE_TYPE is limited private;
  function MIN(QUEUE: QUEUE_TYPE) return ITEM_TYPE;
  -- Returns the smallest item in the queue.
  -- Result is undefined if the queue is empty.
  -- The results of all operations are also undefined for
  -- an uninitialized queue.
  procedure INSERT(QUEUE: QUEUE_TYPE; ITEM: ITEM_TYPE);
  -- If the item is already there, do nothing.
  procedure DELETE(QUEUE: QUEUE_TYPE; ITEM: ITEM_TYPE);
  -- If the item is not there, do nothing.
  function EMPTY(QUEUE: QUEUE_TYPE) return BOOLEAN;
  procedure MAKE_EMPTY(QUEUE: in out QUEUE_TYPE);
  -- This must be called to initialize each queue.
  pragma INLINE(MIN);
  function MEMBER(QUEUE: QUEUE_TYPE; ITEM: ITEM_TYPE) return BOOLEAN;
  generic
    with procedure P(ITEM: ITEM_TYPE);
  procedure APPLY(QUEUE: QUEUE_TYPE);
private
  type QUEUE_RECORD;
  type QUEUE_TYPE is access QUEUE_RECORD;
end RINGS;