1. Perturbation Theory for Linear Operators;Kato,1966
2. Introduction to the theory of linear nonselfadjoint operators;Gohberg;Amer. Math. Soc. Transl.,1969
3. The root vector expansion of a weakly perturbed selfadjoint operator;Marcus;Soviet Math. Dokl.,1962
4. Conditions under which systems of eigenvectors of some losses of operators form a basis;Kacnelson;Functional Anal. Appl.,1967
5. Summability of series in root vectors of nonselfadjoint elliptic operators;Agranovich;Functional Anal. Appl.,1976