1. On the Conjugate Point Condition for the Control Problem;Breakwell,1964
2. Optimization and control of nonlinear systems using the second variation;Breakwell;SIAM J. Control, Ser. A,1963
3. Calculus of Variations;Gelfand,1963
4. The Theory of Optimal Control and the Calculus of Variations;Kalman;RIAS Tech. Rept. No. 61-3,1961