Khachaturyan, Armen. “Necessary Conditions for Optimal Permissible Placement by the Height of the Transitive Directed Tree With One Root (part Second)”. Mathematical Problems of Computer Science 37 (December 10, 2021): 102–107. Accessed February 26, 2026. http://www.mpcs.sci.am/index.php/mpcs/article/view/259.