Operational quantities characterizing semi-Fredholm operators
Volume 114 / 1995
Studia Mathematica 114 (1995), 13-27
DOI: 10.4064/sm-114-1-13-27
Abstract
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.
