Lubis, R. A., and F. A. Sianturi. “Hepatitis Disease Diagnosis Expert System Using Certainty Factor: Hepatitis Disease Diagnosis Expert System Using Certainty Factor”. Jurnal Mantik, vol. 3, no. 3, Nov. 2019, pp. 54-61, https://www.ejournal.iocscience.org/index.php/mantik/article/view/316.