Jacinto, H. ., and S. . Carreira. “Digital Tools and Paper-and-Pencil in Solving-and-Expressing: How Technology Expands a student’s Conceptual Model of a Covariation Problem”. Journal on Mathematics Education, vol. 12, no. 1, Jan. 2021, pp. 113-32, https://jme.ejournal.unsri.ac.id/index.php/jme/article/view/3734.