THUẦN, H.; THÀNH, T. T. SQL query expressed in relational calculus. Journal of Computer Science and Cybernetics, [S. l.], v. 14, n. 4, p. 73–80, 2016. DOI: 10.15625/1813-9663/14/4/7976. Disponível em: https://vjs.ac.vn/index.php/jcc/article/view/7976. Acesso em: 2 may. 2024.