inality of the set <TT><I>s</I></TT>, i.e. the number
      of elements it contains.</P>
    </DD>

    <DT>
      <TT>isEmpty <I>s</I></TT>
    </DT>
    <DD>
      <P>Returns <TT>true</TT> if <TT><I>s</I></TT> is the empty set,
      <TT>false</TT> otherwise. Equivalent to <TT>size <I>s</I> = 0</TT>.</P>
    </DD>

    <DT>
      <TT>member (<I>s</I>, <I>x</I>)</TT>
    </DT>
    <DD>
      <P>Returns <TT>true</TT> if the set <TT><I>s</I></TT> contains an
      element equal to <TT><I>x</I></TT>, <TT>fals