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Operational quantities characterizing semi-Fredholm operators. (English) Zbl 0830.47008

Summary: Several operational quantities have appeared in the literature characterizing upper semi-Fredholm operators. Here, we show that these quantities can be divided into three classes, in such a way that two of them are equivalent if they belong to the same class, and are comparable and not equivalent if they belong to different classes. Moreover, we give a similar classification for operational quantities characterizing lower semi-Fredholm operators.

MSC:

47A53 (Semi-) Fredholm operators; index theories
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