1. The method of averaging in equations with retardation (Russian);Halanay;Rev. Mat. Pur. Appl. Acad. R.P.R.,1959
2. Almost periodic solutions in equations with retardation (Russian);Halanay;Rev. Mat. Pur. Appl. Acad. R.P.R.,1960
3. Averaging Methods for Differential Equations with Retarded Arguments and a Small Parameter;Hale,1964
4. Galerkin's Procedure for Nonlinear Periodic Systems;Urabe,1964
5. Oscillations in Non-Linear Systems;Hale,1963