\Bibitem{Nab91} \by S.~N.~Naboko \paper Structure of the singularities of operator functions with a positive imaginary part \jour Funktsional. Anal. i Prilozhen. \yr 1991 \vol 25 \issue 4 \pages 1--13 \mathnet{http://mi.mathnet.ru/faa892} \mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=1167715} \zmath{https://zbmath.org/?q=an:0764.47003} \transl \jour Funct. Anal. Appl. \yr 1991 \vol 25 \issue 4 \pages 243--253 \crossref{https://doi.org/10.1007/BF01080076} \isi{https://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=Publons&SrcAuth=Publons_CEL&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=A1991HY22000001}