Preliminary Results

We start by reducing M.M. Djrbashian’s general integrodifferential operator \(L_\omega \) used in his factorization theory of functions meromorphic in the unit disc (Djrbashian (Math USSR Izv 2:1027–1065, 1968), Djrbashian (Math USSR Sbornik 8:493–591, 1969), Djrbashian (Theory of factorization and boundary properties of functions meromorphic in the disc. In: Proceedings of the ICM, Vancouver, B.C., 1974, Vol. 2, pp. 197-202, USA, 1975), Djrbashian and Zakarian (Math USSR Izv 4:1273–1354, 1970), Djrbashian and Zakarian (Izv Akad Nauk Arm SSR Matematika 6:182–194, 1971), Djrbashian and Zakarian (Classes and Boundary Properties of Functions Meromorphic in the Disc. Nauka, Moscow, 1993)) to some simple forms, which are used in this book.