[1] E. A. Coddington L. Levinson: Theory of Ordinary Differential Equations. McGraw-Hill, New York 1955. MR 0069338

[2] S. Lefschetz: Differential Equations, Geometric Theory. Interscience Рublishers, New York 1957. MR 0153903 | Zbl 0080.06401

[3] N. Kikuchi: Control problems of contingent equations. Publ. RIMЅ, Kyoto, Ѕer. A, 3 (1967), 85-99. MR 0223696

[4] N. Kikuchi: On some fundamental theorems of contingent equations in connection with the control problems. Publ. RIMЅ, Kyoto, Ѕer. A, 3 (1967), 177-201. MR 0227580 | Zbl 0189.47301

[5] L. Cesari: Existence theorems for weak and usual optimal solutions in Lagrange problems. Part I. Trans. Amer. Math. Ѕoc, Vol. 124, No 3, Ѕeptember 1966, 369-412. MR 0203542

[6] T. Ważewski: On an optimal problem. Proc. of the Conference Equadiff, Prague Ѕeptembeг 1962, 229-242. MR 0201758