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@nate eldredge ,sorry for that as I'm new to the forum I didn't know that issue and when there were no any response to my question in math exchange I thought maybe I had to put it on mathoverflow. For sure it never will repeat again. thanks for notification and I'll be pleased getting information about the diffrence between these two math forum here and the best way to give best answers to my questions.thanks again
Yea ,it seem obvious for simple curve shape like polygons ,even it seem impossible for differentiable curves but there must be a general proof for all curves.
