Sharp generalized Papenfuss-Bach-type inequality

In this paper, we prove and develop a conjecture on the generalized double Papenfuss-Bach inequality proposed by Sun and Zhu [Z. Sun, L. Zhu, J. Appl. Math., 2011 (2011), 9 pages]. In the last section we pose a conjecture on a general form of Papenfuss-Bach-type inequality.