1. D. Suryadi, “Landasan Filosofis Penelitian Desain Didaktis (DDR)” Makalah Bahan Diskusi di Lingkungan Departemen Pendidikan Matematika FPMIPA UPI, 2018.
2. W. Cockcroft, Mathematics Counts (Her Majesty’s Stationery Office, London, 1982), pp. 1–311.
3. D. L. Sulistiowati, T. Herman, and A. Jupri, “Student difficulties in solving geometry problem based on Van Hiele thinking level,” in International Conference on Mathematics and Science Education 2018 IOP Conf. Ser. J. Phys, 1157, (IOP Publishing, Philadelphia, 2019).
4. N. Arifin, E. Nuraeni, and O. Pranata, PEDADIDAKTIKA, 1, 96–102 (2014).
5. Suparyan, “Kajian Kemampuan Keruangan (Spatial Abilities) dan Kemampuan Penguasaan Materi Geometri Ruang,” thesis, Universitas Negeri Semarang, 2007.