Thaweedet Yantassanavanich. (2007) Vanishing sum and roots of unity /. Kasetsart University,:ม.ป.ท.Thaweedet Yantassanavanich. 2007. Vanishing sum and roots of unity /. ม.ป.ท.:Kasetsart University,;Thaweedet Yantassanavanich. Vanishing sum and roots of unity /. ม.ป.ท.:Kasetsart University, 2007. Print.