Kondratyuk, Y. V. “On the Boundedness of the Total Variation of the Logarithm of a Blaschke Product”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 51, no. 11, Nov. 1999, pp. 1449–1455, https://umj.imath.kiev.ua/index.php/umj/article/view/4746.