Fushchich W. I., and Zhdanov R. Z. “Conditional Symmetry and Reduction of Differential Equations With Partial Derivatives ”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 7 (August 3, 1992): 970-982. Accessed October 6, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/8129.