Lubis SEF, Saragi D, Yunita S. Development of problem-solving-based digital books to improve students’ high-level thinking skills. Inov. Curr [Internet]. 2024 Nov. 29 [cited 2026 Aug. 16];21(4):2075-88. Available from: https://ejournal-hipkin.or.id/index.php/jik/article/view/618