1. Perturbations and approximations of continuous optimal control problems;Cullum,1967
2. Perturbations of optimal control problems;Cullum;SIAM J. Control Optim.,1966
3. On the correctness of the formulation of an optimal control problem;Kirillova;SIAM J. Control Optim.,1963
4. On the stability of minimum points;Hyers;J. Math. Anal. Appl.,1978
5. Non-Linear Differential Equations;Sansone,1964