Partial isometries and generalized inverses of linear relations

Abstract

For a closed linear relation everywhere defined on a Hilbert space the concepts of isometry, co-isometry, partial isometry, and generalized inverse are introduced and studied. Part of the results proved in this paper improve and generalize some results known for these concepts. In particular, we extend those of [Acta Sci. Math. (Szeged), 70 (2004), 767–781] and [Studia Math. 205 (2011), no. 1, 71–82].