Gorbachuk, V. I., and M. L. Gorbachuk. 1997. “Behavior of the Extended Spectral Measure of a Self-Adjoint Operator at Infinity”.
Ukrains’kyi Matematychnyi Zhurnal
49 (4): 510–516.
https://umj.imath.kiev.ua/index.php/umj/article/view/5024
.