Nyamsuren, Enkhbold, Han van der Maas, and Matthias Maurer. “Set-Theoretical and Combinatorial Instruments for Problem Space Analysis in Adaptive Serious Games”. International Journal of Serious Games 5, no. 1 (March 26, 2018). Accessed December 15, 2018. http://journal.seriousgamessociety.org/index.php/IJSG/article/view/219.