Afshari, H., S. Rezapour, and N. Shahzad. “Absolute Retractivity of the Common Fixed Points Set of Two Multifunctions”. Topological Methods in Nonlinear Analysis, vol. 40, no. 2, Apr. 2012, pp. 429-36, https://apcz.umk.pl/TMNA/article/view/TMNA.2012.040.