@article{IM2_1998_62_5_a2,
     author = {O. A. Danilova and A. S. Matveev},
     title = {Non-traditional conditions for the existence of an optimal control for the {Goursat--Darboux} equations},
     journal = {Izvestiya. Mathematics },
     pages = {929--951},
     publisher = {mathdoc},
     volume = {62},
     number = {5},
     year = {1998},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1998_62_5_a2/}
}