@article{SM_1977_31_2_a9,
     author = {N. N. Frolov},
     title = {On the hypoellipticity of infinite-dimensional differential operators},
     journal = {Sbornik. Mathematics},
     pages = {269--278},
     year = {1977},
     volume = {31},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1977_31_2_a9/}
}