Osipchuk Т. М. “Topological and Geometric Properties of the Set of 1-Nonconvexity Points of a Weakly 1-Convex Set in the Plane”. Ukrains’kyi Matematychnyi Zhurnal, vol. 73, no. 12, Dec. 2021, pp. 1657-72, https://doi.org/10.37863/umzh.v73i12.6890.