Dudkin, M. Ye. “Analog of the Krein Formula for Resolvents of Normal Extensions of a Prenormal Operator”.
Ukrains’kyi Matematychnyi Zhurnal
, vol. 54, no. 4, Apr. 2002, pp. 555-62,
https://umj.imath.kiev.ua/index.php/umj/article/view/4092
.