1. Zeros of the Wronskian and renormalized oscillation theory;Gesztesy;Amer. J. Math.,1996
2. Traces and Determinants of Linear Operators;Gohberg,2000
3. Perturbation Theory for Linear Operators;Kato,1966
4. Perturbation determinants and a formula for the traces of unitary and self-adjoint operators;Krein;Soviet Math. Dokl.,1962