Abstract
The paper deals with unbounded hyponormal operators. Among others it is proved that any closed hyponormal operator with spectrum contained in a parabola generates a cosine function.
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Janas, J. On unbounded hyponormal operators II. Integr equ oper theory 15, 470–478 (1992). https://doi.org/10.1007/BF01200330
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DOI: https://doi.org/10.1007/BF01200330