1. L.C. Becker, Stability considerations for Volterra integro-differential equations, Ph.D. Dissertation, Southern Illinois University, Carbondale, IL, 1979. (A PDF version of the entire dissertation can be found at the Web site: http://www.cbu.edu/~lbecker/Research.htm.)
2. Stability Theory of Differential Equations;Bellman,1953
3. Stability and Periodic Solutions of Ordinary and Functional Differential Equations;Burton,2005
4. Volterra Integral and Differential Equations;Burton,2005