Arliansyah Maulana. Teori Perkembangan Kognitif Piaget Pada Tahap Operasional Formal. Ahnaf [Internet]. 2024 Jul. 18 [cited 2026 Oct. 22];1(1):12-21. Available from: https://mail.al-ahnaf.my.id/index.php/i/article/view/7