M. Kaltenbäck, H. Winkler, H. Woracek:
"Generalized Nevanlinna functions with essentially positive spectrum";
J. Operator Theory, 55 (2006), 1; S. 17 - 48.
http://aleph.ub.tuwien.ac.at/F?base=tuw01&func=find-c&ccl_term=AC06587924
Projektleitung Heinz Langer:
RTN Analysis and Operators