“…It is important that three out of four conditions in this characterization follow from the Zakharov-Faddeev trace formula (4.7) below, which is extended in [20] to L 2 potentials, all conditions being very mild. On the other hand, detailed descriptions of the Jost solution, the Weyl m-function, and the spectral measure 7 of the half-line (Dirichlet) Schrodinger operator with WvN type potentials (and their sums, finite or even infinite) are given in [17,22] (see section 4). This way we construct two spectral measures ρ ± (E) with a desirable behavior for E > ε > 0.…”