ON A GENERALIZATION OF THE KALMAN-YAKUBOVIC LEMMA

In this paper we generalize the Kalman-Yakubovic lemma to infinite dim ensions - or, more precisely, to semigroups of operators over a Hilber t space. The proof differs substantially from the finite-dimensional v ersion and is based on the Paley-Wiener-Helson-Lowdenslager factorizat ion theorem.