1. Factorization of ordinary differential operators that can be transformed into operators with constant coefficients;Berkovic;Izv. Vysš. Učebn. Zaved. Mat.,1965
2. Factorization of ordinary linear differential operators that can be transformed into operators with constant coefficients II;Berkovic;Izv. Vysš. Učebn. Zaved. Mat.,1967
3. The reduction of ordinary linear differential equations to equations with constant coefficients;Berkovic;Volz. Mat. Sb.,1966
4. Ordinary Differential Equations;Ince,1956
5. Calculus of Finite Differences;Jordan,1960