Yuster, Raphael. “The Covering Threshold of a Directed Acyclic Graph by Directed Acyclic Subgraphs”. The Electronic Journal of Combinatorics 29, no. 4 (December 16, 2022): P4.45. Accessed March 16, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v29i4p45.