Alfaro-Carvajal, Cristian, and Jennifer Fonseca-Castro. “Problem Solving in the Teaching of Single Variable Differential and Integral Calculus: Perspective of Mathematics Teachers”. Uniciencia 32, no. 2 (July 25, 2018): 42-56. Accessed October 20, 2019. https://www.revistas.una.ac.cr/index.php/uniciencia/article/view/10658.