VO, Duc Thinh. The directionally normal cone and optimal condition. Dong Thap University Journal of Science, [S. l.], n. 13, p. 63–68, 2015. DOI: 10.52714/dthu.13.6.2015.206. Disponível em: https://dthujs.vn/index.php/dthujs/article/view/816. Acesso em: 8 sep. 2024.