@article{SM_1989_64_2_a11,
     author = {N. M. Gulevich and S. V. Konyagin and R. V. Rakhmankulov},
     title = {Fixed points and differentiability of the norm},
     journal = {Sbornik. Mathematics},
     pages = {461--469},
     year = {1989},
     volume = {64},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1989_64_2_a11/}
}