Bezkorovaina, L. L., and T. Yu. Vashpanova. 2010. “$A$-Deformations of a Surface With Stationary Lengths of $LGT$-Lines”. Ukrains’kyi Matematychnyi Zhurnal 62 (7), 878–884. https://umj.imath.kiev.ua/index.php/umj/article/view/2921.