@article{MT_2014_17_2_a2,
     author = {V. N. Berestovskiǐ and I. A. Zubareva},
     title = {Functions with (non)timelike gradient on a~space-time},
     journal = {Matemati\v{c}eskie trudy},
     pages = {41--60},
     publisher = {mathdoc},
     volume = {17},
     number = {2},
     year = {2014},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MT_2014_17_2_a2/}
}