Severino, Michael. “A Construction of Uniquely $n$-Colorable Digraphs With Arbitrarily Large Digirth”. The Electronic Journal of Combinatorics 24, no. 2 (April 13, 2017): P2.1. Accessed March 17, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v24i2p1.