Díaz-Parra, O., A. Fuentes-Penna, M. A. Ruiz-Jaimes, Y. Toledo-Navarro, M. Lezama-León, and E. Lezama-León. “Intelligent Tutor System for the Learning of Otomí Language”. International Journal of Combinatorial Optimization Problems and Informatics, vol. 9, no. 3, Mar. 2018, pp. 18-25, https://ijcopi.org/ojs/article/view/97.