A characterization of closed range operators
The paper under review contains three proofs for the fact that, if \(T\) is a bounded linear operator between some complex Hilbert spaces, then it has closed range if and only if \(0\) is not an accumulation point for the spectrum of \(T^*T\). The proofs are ``applications of different concepts in basic operator theory'' (in authors' words).
scientific article; zbMATH DE number 1484567