1. Stability of nonautonomous systems by Liapunov's direct method;Aeyels,1993
2. D. Aeyels and R. Sepulchre, On the convergence of a time-variant linear differential equation arising in identification, to appear in Kybernetika.
3. Stability of motion in the large;Barbashin;Dokl. Akad. Nauk SSSR,1952
4. Foundations of Modern Analysis;Dieudonné,1969
5. Nonlinear Systems;Khalil,1992