E. A. . Sari, K. . Hadiprasetyo, and A. A. . Wulandari, “Learning difficulties of mathematic students on real analysis courses with an online system”, J. Math Educ. Nusant. Wahana Publ. Karya Tulis Ilm. di Bid. Pendidik. Mat., vol. 7, no. 1, pp. 1–11, May 2021.