Helge Krueger and Gerald Teschl
Relative Oscillation Theory for Sturm-Liouville Operators Extended
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ABSTRACT.  We extend relative oscillation theory to the case of Sturm--Liouville operators 
$H u = r^{-1}(-(pu')'+q u)$ 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.