Hastuti, Sri, et al. “The Effectiveness of Applying E-Book in Teaching Indonesian to Speakers of Other Languages (TISOL) in Supporting Foreign Students’ Self-Learning in Indonesia”. International Journal of Engineering & Technology, vol. 7, no. 3.4, June 2018, pp. 277-9, https://doi.org/10.14419/ijet.v7i3.4.20118.