Dymarskii, Ya. M. “On Manifolds of Eigenfunctions and Potentials Generated by a Family of Periodic Boundary-Value Problems”. Ukrains’kyi Matematychnyi Zhurnal 48, no. 6 (June 25, 1996): 771–781. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/5277.