1. R. Bellman and J. M. Danskin, Jr., A Survey of the Mathematical Theory of Time-lag, Retarded Control, and Hereditary Processes, The RAND Corporation, Report R-256, March 1, 1954. §13.1. The results of this chapter were previously given in the monograph
2. On the Zeros of Some Elementary Transcendental Functions;Pontrjagin;Izv. Akad. Nauk SSSR, Ser. Mat.,1942
3. On the zeros of some transcendental functions
4. The Routh-Hurwitz Problem for Polynomials and Entire Functions;čebotarev;Trudy Mat. Inst. Steklov,1949
5. Roots of the Transcendental Equation Associated with a Certain Difference-differential Equation;Hayes;J. London Math. Soc.,1950