Siggers, Mark. “Reflexive Graphs With Near Unanimity But No Semilattice Polymorphisms”. The Electronic Journal of Combinatorics 25, no. 4 (October 5, 2018): P4.2. Accessed March 17, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v25i4p2.