2>
<p>An <i>UpdatablePriorityQueue</i> is a slight refinement of <a href="#concept%3AUpdatableQueue">UpdatableQueue</a>
that imposes the requirement that a program may not increase the position of a value that is held in the queue. That is,
if a value <tt>v</tt> had position <i>n</i> in the ordering, a program may update the position of <tt>v</tt> only to 0, 1, ..., <i>n</i>&nbsp;-&nbsp;1, or <i>n</i>, where 0 is the top of the queue.

<p>The behavior when a program attempts to increase a value's position i