Gorbachuk, V. I., and M. L. Gorbachuk. “Behavior of the Extended Spectral Measure of a Self-Adjoint Operator at Infinity”. Ukrains’kyi Matematychnyi Zhurnal, vol. 49, no. 4, Apr. 1997, pp. 510–516, https://umj.imath.kiev.ua/index.php/umj/article/view/5024.