OSUAGWU, C. Elements, ordered arrangements and systems. International Journal of Natural and Applied Sciences, [S. l.], v. 2, n. 3, p. 283–286, 2007. DOI: 10.4314/ijonas.v2i3.36105. Disponível em: https://www.ajol.info/index.php/ijonas/article/view/36105. Acesso em: 16 oct. 2026.