Relative oscillation theory for Sturm–Liouville operators extended

We extend relative oscillation theory to the case of Sturm–Liouville operators Hu = r−1(−(pu ) +qu) with different p’s. We show that the weighted number of zeros of Wronskians of certain solutions equals the value of Krein’s spectral shift function inside essential spectral gaps. © 2007 Elsevier Inc. All rights reserved