Fushchich, V. I. “Symmetry of Equations of Linear and Nonlinear Quantum Mechanics”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 1 (January 25, 1997): 164–176. Accessed April 14, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/4994.