Tomno, Victor, Fredrick Nyamwala, and Waweru Kamaku. 2018. “The Wss P0 Matrix Completion Problem for Symmetric Patterns of Acyclic Digraphs of Order Four”. International Journal of Sciences: Basic and Applied Research (IJSBAR) 37 (1): 112-21. https://www.gssrr.org/JournalOfBasicAndApplied/article/view/8591.