1. Completeness of the system of Floquet solutions of linear first order differential equations with delays that are multiples of the period of the coefficients;Gurari;Vestnik Kharkov Gos. Univ.,1971
2. “Functional Differential Equations.”;Hale,1971
3. Completeness of the system of Floquet solutions of equations of the neutral type;Kuleski;Mat. Zemethi,1968
4. Periodic differential difference equations;Lillo;J. Math. Anal. Appl.,1966
5. The Green's function for periodic differential difference equations;Lillo;J. Differential Equations,1968