Linear combinations of isometries (Q1880975)

Let \(MI\) denote the set of all scalar multiples of all isometries in a Hilbert space \(H\). In this paper, the authors investigate finite-dimensional linear spaces contained in \(MI\) and the commutativity of such spaces. The authors also present an example of two unilateral shifts \(A\), \(B\) of infinite multiplicity such that span\((A,B)\subset MI\) and \(A\), \(B\) do not commute.