Hendriana, H., R. C. I. Prahmana, and W. Hidayat. “The Innovation of Learning Trajectory on Multiplication Operations for Rural Area Students in Indonesia”. Journal on Mathematics Education, vol. 10, no. 3, Sept. 2019, pp. 397-08, https://jme.ejournal.unsri.ac.id/index.php/jme/article/view/3802.