HUY, N. X. A labelling operator and relational operations. Journal of Computer Science and Cybernetics, [S. l.], v. 1, n. 3, p. 1–7, 2015. DOI: 10.15625/1813-9663/1/3/6687. Disponível em: https://vjs.ac.vn/index.php/jcc/article/view/6687. Acesso em: 28 apr. 2024.