Geodesic
On continuity of the spectrum of a~singular quasi-differential operator with respect to a~parameter
Eurasian mathematical journal, Tome 2 (2011) no. 3, pp. 67-81.

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We obtain sufficient conditions for continuity of the eigenvalues of semibounded quasi-differential operators of order $2n$ on the half-axis with respect to the parameters that appear in the corresponding differential expression. In addition we obtain a generalization of the well-known result of M. G. Krein [9] concerning description of the quadratic form of a regular quasi-differential operator in the singular case, when the deficiency indices of the minimal operator are equal to $(n,n)$. 
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Kh. K. Ishkin. On continuity of the spectrum of a~singular quasi-differential operator with respect to a~parameter. Eurasian mathematical journal, Tome 2 (2011) no. 3, pp. 67-81. http://geodesic.mathdoc.fr/item/EMJ_2011_2_3_a3/

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