@article{SM_1980_37_1_a1,
     author = {A. V. Babin},
     title = {Fractional powers of a~nonlinear analytic differential operator},
     journal = {Sbornik. Mathematics},
     pages = {9--38},
     year = {1980},
     volume = {37},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1980_37_1_a1/}
}