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Generating real maps on a biordered set. (English) Zbl 0757.47013

Operational quantities have been derived from the norm of operators between Banach spaces. For example, given an operator \(T\) between Banach spaces \(X\) and \(Y\), \(\text{in}(T)\) is defined as the infimum of the operator norms of \(TJ_ M\) over all infinite dimensional closed subspaces \(M\), where \(J_ M\) denotes the injection of the subspace \(M\) into \(X\). This has in turn been used to characterize upper semi-Fredholm operators. In an effort to generalize this type of construction, the author considers the abstract setting of maps from a set \(X\) with two orders related by certain properties. This is called a biordered space. If an initial map is bounded and monotone, then it is established that only three different new maps can be derived using the infimum and supremum.

MSC:

47A53 (Semi-) Fredholm operators; index theories
06A06 Partial orders, general
47A30 Norms (inequalities, more than one norm, etc.) of linear operators