Vílchez Quesada, Enrique, and Juan Ávila Herrera. “Factótum Virtual Tutor for the Study of the Functions”. Uniciencia 27, no. 1 (January 1, 2013): 119-139. Accessed May 7, 2021. https://www.revistas.una.ac.cr/index.php/uniciencia/article/view/4946.