1. Degenerate problems of Optimal Control;Gurman,1977
2. Sufficient Stromg minimum Conditions of Singular and Sliding Regimes;Gurman;Dlfferenzialnye ïïravneniya,1976
3. Sufficient Strong Extremum Conditions for Singular Regimes of Optimal Control;Dykhta,1977
4. Methods and Problems of Optimal Control;Krotov,1973