Widiyaningsih, Endang, Zaenuri Zaenuri, and Dwijanto Dwijanto. 2020. “Problem-Solving Ability and Self-Efficacy Based On Geometry Thinking Level In Van Hiele Learning”. Unnes Journal of Mathematics Education Research 9 (2), 163-69. http://journal.unnes.ac.id/sju/ujmer/article/view/33118.