Prykarpatsky, A. K., and V. G. Samoilenko. 2004. “Structure of Binary Darboux-Type Transformations for Hermitian Adjoint Differential Operators”. Ukrains’kyi Matematychnyi Zhurnal 56 (2), 271-75. https://umj.imath.kiev.ua/index.php/umj/article/view/3751.