Faculty of Industrial Technologies in Púchov, Alexander Dubček University in Trenčín, I. Krasku 491/30, 02001 Púchov, Slovakia
Academic Editor: Sin E. Takahasi
Copyright © 2010 Ladislav Matejíčka. This is an open access article distributed under the
Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Two open problems
were posed in the work of Long and Chu (2010). In this paper, we give the
solutions of these problems.