On July 3rd, 1996 Barak Pearlmutter (bap@valaga.salk.edu) gives me an another trick for getting |x| that is
Thanks for the suggestion. I should notice this trivial trick. I wonder why I did not use it... By using this idea, the equation (4) can be substituted by more sophisticated manner which is
I think this expression could be called "perfect" as a expression of n-gon.