T>
    <DD>
      <P>Applies <TT><I>f</I></TT> to each element <TT><I>x</I></TT> of set
      <TT><I>s</I></TT> and returns the set of elements for which
      <TT><I>f x</I></TT> delivered <TT>true</TT>.
      For red-black trees, <TT><I>f</I></TT> is applied in increasing order.
      Equivalent to
      <TT>fromList(List.filter <I>f</I> (toList <I>s</I>))</TT>.</P>
    </DD>

    <DT>
      <TT>partition <I>f</I> <I>s</I></TT>
    </DT>
    <DD>
      <P>Applies <TT><I>f</I></TT> to each element <TT><I>x