Kofanov, V. “Bojanov–Naidenov Problem for Differentiable Functions and the Erdös Problem for Polynomials and Splines”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 75, no. 2, Mar. 2023, pp. 182 -97, doi:10.37863/umzh.v75i2.7259.