Indicates an attempt to add an item that already is in the set
      when using functions that disallow replacement.</P>
    </DD>

    <DT>
      <TT>empty</TT>
    </DT>
    <DD>
      <P>The empty set.</P>
    </DD>

    <DT>
      <TT>singleton <I>x</I></TT>
    </DT>
    <DD>
      <P>The set only containing the value <TT><I>x</I></TT>.</P>
    </DD>

    <DT>
      <TT>fromList <I>l</I></TT>
    </DT>
    <DD>
      <P>Returns the set containing the elements from list <TT><I>l</I></TT>.
      Raises <