Fredy Gavilanes-Sagnay, Edison Loza-Aguirre, Byron Ernesto Vaca Barahona, Henry N. Roa, “A Systematic Review of Ill-Defined Problems in the Intelligent Tutoring Systems in Virtual Learning Environments”, Int J Intell Syst Appl Eng, vol. 11, no. 5s, pp. 220 –, Apr. 2023.