GHT="16" ALIGN="MIDDLE" BORDER="0"
 SRC="img44.png"
 ALT="$f_1$">
is a function of  three variables, the  function itself is really only
composed of <EM>two</EM> independent parts; the product of <!-- MATH
 $v_1 + v_2 - 2
v_3$
 -->
<IMG
 WIDTH="91" HEIGHT="15" ALIGN="MIDDLE" BORDER="0"
 SRC="img45.png"
 ALT="$v_1 + v_2 - 2
v_3$"> with <IMG
 WIDTH="42" HEIGHT="12" ALIGN="BOTTOM" BORDER="0"
 SRC="img46.png"
 ALT="$e^{v_1 - v_3}$">, or, if we write <!-- MATH
 $u_1 = v_1  +  v_2 - 2 v_3$
 -->
<IMG
 WIDTH="128" 