Nur Permadi, Riki, Agus Abadi, and Fitri Asanti. “APOS Theory-Based Learning: Impact on Mathematical Problem-Solving Skills”. International Journal Of Mathematics And Computer Research 13, no. 7 (July 11, 2025): 5407-5411. Accessed May 19, 2026. https://www.ijmcr.everant.org/index.php/ijmcr/article/view/990.