文摘
We extend the basic elements of Clark's theory of rank-one perturbations of backward shifts, to row-contractive operators associated to de Branges-Rovnyak type spaces contrastively contained in the Drury-Arveson space on the unit ball in . The Aleksandrov-Clark measures on the circle are replaced by a family of states on a certain noncommutative operator system, and the backward shift is replaced by a canonical solution to the Gleason problem in . In addition we introduce the notion of a 鈥渜uasi-extreme鈥?multiplier of the Drury-Arveson space and use it to characterize those spaces that are invariant under multiplication by the coordinate functions.