theorem
  for r1, r2, r3 being Complex holds Product <*r1,r2,r3*> = r1 * r2 * r3
proof
  let r1, r2, r3 be Complex;
  thus Product <*r1,r2,r3*> = Product <*r1,r2*> * r3 by Th96
    .= r1 * r2 * r3 by Th99;
end;
