Kitahara, S., and W. Takahashi. “Image Recovery by Convex Combinations of Sunny Nonexpansive Retractions”. Topological Methods in Nonlinear Analysis, vol. 2, no. 2, Dec. 1993, pp. 333-42, https://apcz.umk.pl/TMNA/article/view/TMNA.1993.046.