Linear Relations in Hilbert Spaces
Jussi Behrndt, Seppo Hassi, Henk S. V. de Snoo · Monographs in mathematics · 2020
A linear relation from one Hilbert space to another Hilbert space is a linear subspace of the product of these spaces. In this chapter some material about such linear relations is presented and it is shown how linear operators, whether densely defined or not, fit in this context.