Sheikholeslami, Seyed Mahmoud, Asghar Bodaghli, and Lutz Volkmann. “Twin Signed Roman Domination Numbers in Directed Graphs”. Tamkang Journal of Mathematics 47, no. 3 (September 30, 2016): 357–371. Accessed April 26, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/2035.