Čupona, Ǵ., and S. Markovski. “EMBEDDINGS OF UNIVERSAL ALGEBRAS IN SEMIGROUPS”. Matematichki Bilten 15, no. 1 (January 1, 1991): 5–16. Accessed October 19, 2026. https://bilten.smm.org.mk/index.php/bilten/article/view/1499.