// Textbook fragment 08.08
  /** Returns but does not remove an entry with minimum key. */
  public Entry<K,V> min () throws EmptyPriorityQueueException {
    if (entries.isEmpty())
      throw new EmptyPriorityQueueException("priority queue is empty");
    else
      return entries.first().element();
  }
  /** Inserts a key-value pair and return the entry created. */
  public Entry<K,V> insert (K k, V v) throws InvalidKeyException {
    checkKey(k); // auxiliary key-checking method (could throw exception)
    Entry<K,V> entry = new MyEntry<K,V>(k, v);
    insertEntry(entry);               // auxiliary insertion method
    return entry;
  }
  /** Auxiliary method used for insertion. */
  protected void insertEntry(Entry<K,V> e) {
    if (entries.isEmpty()) {
      entries.addFirst(e);            // insert into empty list
      actionPos = entries.first();    // insertion position
    }
    else if (c.compare(e.getKey(), entries.last().element().getKey()) > 0) {
      entries.addLast(e);             // insert at the end of the list
      actionPos = entries.last();     // insertion position
    }
    else {
      Position<Entry<K,V>> curr = entries.first();
      while (c.compare(e.getKey(), curr.element().getKey())> 0) {
        curr = entries.next(curr);    // advance toward insertion position
      }
      entries.addBefore(curr, e);
      actionPos = entries.prev(curr); // insertion position
    }
  }
  /** Removes and returns an entry with minimum key. */
  public Entry<K,V> removeMin() throws EmptyPriorityQueueException {
    if (entries.isEmpty())
      throw new EmptyPriorityQueueException("priority queue is empty");
    else
      return entries.remove(entries.first());
  }