[1] E. B. Lee L. Markus:
Foundations of Optimal Control Theory. John Wiley and Sons, Inc., New York 1967.
MR 0220537
[2] H. Hermes J. P. La Salle:
Functional Analysis and Time Optimal Control. Academic Press, New York 1969.
MR 0420366
[3] F. E. Nixon: Principles of Automatic Controls. MacMillan & Co. Ltd., London 1958.