RUẬN, Đặng H.; ỔN, P. V. Some properties of context free hyper-languages. Journal of Computer Science and Cybernetics, [S. l.], v. 16, n. 2, p. 5–8, 2013. DOI: 10.15625/1813-9663/16/2/2866. Disponível em: https://vjs.ac.vn/index.php/jcc/article/view/2866. Acesso em: 7 may. 2024.