Buldygin, V. V., and V. V. Pavlenkov. “Karamata Theorem for Regularly Log-Periodic Functions”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 64, no. 11, Nov. 2012, pp. 1443-6, https://umj.imath.kiev.ua/index.php/umj/article/view/2672.