1. Singular extremals;Kelley,1966
2. Singular solutions in optimal control problems;Johnson,1965
3. The second variation of the singular Bolza problem;Goh;SIAM J., Ser. A: Control,1966
4. Necessary conditions for singular extremals involving multiple control variables;Goh;SIAM J., Control,1966
5. Necessary conditions for singular extremals in the calculus of variations;Goh;Ph. D. Thesis,1966