1. Boltjanskii, V., Gamkrelidze, R, and Pontijagin, L. (1956): On the theory of optimal processes. Doklady Akad. Nauk SSSR 110 (7–10) (Russian).
2. Gamkrelidze, R. (1958): Theory of time-optimal processes for linear systems. Izv. Akad. Nauk SSSR, ser. mat. 22 (449–474) (Russian).
3. Boltjanskii, V. (1958): The maximum principle and the theory of optimal processes. Doklady Akad. Nauk SSSR 119 (1070–1073) (Russian).
4. Pontijagin, L. (1959): Optimal control processes. Uspehi Mat. Nauk 14, 1 (3–20) (Russian).
5. Hestenes, M. (1950): A general problem in the calculus of variations with applications to paths of least time. The Rand Corporation, Santa Monica, CA.