Yavorskii, Y.M. (1994) “Estimation of eigenvalues of self-adjoint operators”,
Ukrains’kyi Matematychnyi Zhurnal
, 46(5), pp. 642–648. Available at:
https://umj.imath.kiev.ua/index.php/umj/article/view/5725
(Accessed: 10 April 2025).