@article{IM2_1968_2_6_a7,
     author = {M. I. Freidlin},
     title = {On the smoothness of solutions of degenerate elliptic equations},
     journal = {Izvestiya. Mathematics},
     pages = {1337--1359},
     year = {1968},
     volume = {2},
     number = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1968_2_6_a7/}
}