Ušan, Janez. “ON \((k(n-1)+1)\)-SEMIGROUPS WITH \((n-2)\)-NEUTRAL OPERATIONS”. Matematichki Bilten 22, no. 1 (January 1, 1998): 5–14. Accessed August 14, 2026. https://bilten.smm.org.mk/index.php/bilten/article/view/1583.