@article{DAN_1991_320_2_a7,
     author = {V. I. Sumin},
     title = {Strong degeneration of singular controls in distributed problems},
     journal = {Doklady Akademii Nauk},
     pages = {295--299},
     publisher = {mathdoc},
     volume = {320},
     number = {2},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1991_320_2_a7/}
}