@article{IM2_1988_30_2_a13,
     author = {A. L. Sakhnovich},
     title = {On~a~class of extremal problems},
     journal = {Izvestiya. Mathematics },
     pages = {411--418},
     publisher = {mathdoc},
     volume = {30},
     number = {2},
     year = {1988},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1988_30_2_a13/}
}