@article{IM2_2000_64_4_a5,
     author = {A. A. Tolstonogov},
     title = {A~theorem of existence of an optimal control for the {Goursat--Darboux} problem without convexity assumptions},
     journal = {Izvestiya. Mathematics },
     pages = {807--826},
     publisher = {mathdoc},
     volume = {64},
     number = {4},
     year = {2000},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_2000_64_4_a5/}
}