T>
      <TT>future <I>h</I></TT>
    </DT>
    <DD>
      <P>Returns the future associated with the hole <TT><I>h</I></TT>. If
      <TT><I>h</I></TT> is not a hole, <TT>h</TT> is returned.</P>
    </DD>

    <DT>
      <TT>fill (<I>h</I>, <I>v</I>)</TT>
    </DT>
    <DD>
      <P>Replaces the hole <TT><I>h</I></TT> and its associated future with
      the value <TT><I>v</I></TT>. If <TT><I>v</I></TT> is the hole or its
      future itself, the exception <TT>Future.Cyclic</TT> is raised instead.
      If 