Nurlaily, V. A., H. Soegiyanto, and B. Usodo. “Elementary School teacher’s Obstacles in the Implementation of Problem-Based Learning Model in Mathematics Learning”. Journal on Mathematics Education, vol. 10, no. 2, May 2019, pp. 229-38, https://jme.ejournal.unsri.ac.id/index.php/jme/article/view/3790.