J. Cihlář, P. Eisenmann, M. Krátká, and P. Vopĕnka, “Cognitive conflict as a tool of overcoming obstacles in understanding infinity”, Teach. Math. Comp. Sci., vol. 7, no. 2, pp. 279–295, Dec. 2009, doi: 10.5485/TMCS.2009.0240.