Estimates for periodic eigenvalues of the differential operator $(-1)^md^2m/dx^2m+V$ with $V$-distribution

Molyboga, V. M. “Estimates for Periodic Eigenvalues of the Differential Operator $(-1)^md^2m Dx^2m+V$ With $V$-Distribution”. Methods of Functional Analysis and Topology, vol. 9, no. 2, June 2003, pp. 163-78, https://zen.imath.kiev.ua/index.php/mfat/article/view/212.