Vasiliev , A. Yu. “Quasi-Variance of the Modulus of Homotopical Classes of Curves and Teichmuller’s Problem”. Ukrains’kyi Matematychnyi Zhurnal, vol. 43, no. 3, Feb. 1991, pp. 329-36, https://umj.imath.kiev.ua/index.php/umj/article/view/9611.