Completeness of the system of root vectors of operators in a space with indefinite metric
T. Ya. Azizov

References
1.	Gokhberg I.Ts., Krein M.G., Vvedenie v teoriyu lineinykh nesamosopryazhennykh operatorov v gilbertovom prostranstve, Nauka, M., 1965
2.	Azizov T.Ya., Iokhvidov I.S., Osnovy teorii lineinykh operatorov v prostranstvakh s indefinitnoi metrikoi, Nauka, M., 1968