Čupona, Ǵorǵi, Naum Celakoski, and Biljana Janeva. 1999. “CANONICAL GROUPOIDS WITH \(x^m \cdot y^n = xy\)”. Matematichki Bilten 23 (1): 11-18. https://bilten.smm.org.mk/index.php/bilten/article/view/1592.