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4. Khromov, A.P.: Konechnomernye vozmushcheniya vol’terrovykh operatorov. Diss. dokt. fiz.-mat. nauk [Finite-dimensional perturbations of Volterra operators: Dr. phys. and mat. sci. diss.]. Novosibirsk (1973) (in Russian)
5. Shkalikov, A.A.: O polnote sobstvennykh i prisoedinennykh funktsii obyknovennogo differentsial’nogo operatora s nereguliarnymi kraevymi usloviiami [On completenes of eigenfunctions and associated function of an ordinary differential operator with separated irregular boundary conditions]. Funktsional. Anal. i Prilozhen. [Functional analysis and applications] 10(4), 69–80 (1976) (in Russian)