“Exact and Approximate Solutions of the Spectral Problems for the Differential Schrödinger Operator With a Polynomial Potential in ${\mathbb R}^{k}$, $k\ge 2$”. Neliniini Kolyvannya 21, no. 1 (March 29, 2018): 66–98. Accessed January 21, 2026. https://twinhead.imath.kiev.ua/index.php/nosc/article/view/897.