</TD>
<TD WIDTH=10 ALIGN="RIGHT">
(2.7)</TD></TR>
</TABLE>
<BR CLEAR="ALL"></DIV><P></P>
where for example  <IMG
 WIDTH="52" HEIGHT="11" ALIGN="MIDDLE" BORDER="0"
 SRC="img54.png"
 ALT="$v_1 = x_6$"> and  <IMG
 WIDTH="58" HEIGHT="10" ALIGN="MIDDLE" BORDER="0"
 SRC="img55.png"
 ALT="$v_2 = x_{12}$">.  Here, we  have
broken <IMG
 WIDTH="14" HEIGHT="16" ALIGN="MIDDLE" BORDER="0"
 SRC="img56.png"
 ALT="$f_2$"> down  into as few  pieces as possible. Although there are
internal variables, <IMG
 WIDTH="51" HEIGHT=