Dymarskii, Ya. M. 2001. “On the Manifolds of Eigenvectors of Linear and Quasilinear Finite-Dimensional Self-Adjoint Operators. I”. Ukrains’kyi Matematychnyi Zhurnal 53 (2): 156-67. https://umj.imath.kiev.ua/index.php/umj/article/view/4232.