theorem Th26:
  (the multF of K) $$ <* a,b,c *> = a * b * c
proof
  (the multF of K) $$ <* a,b,c *> = Product <* a,b,c *> by GROUP_4:def 2
    .= a * b * c by FVSUM_1:79;
  hence thesis;
end;
