BAC, Pham Hai. An approach to expanding relational algebra. <b>Journal of Computer Science and Cybernetics</b>, <i>[S. l.]</i>, v. 1, n. 4, p. 20–23, 2015. DOI: 10.15625/1813-9663/1/4/6701. Disponível em: https://jcc.vast.vn/jcc/article/view/6701. Acesso em: 4 nov. 2025.