@article{DAN_1968_181_5_a5,
     author = {N. H. Ibragimov},
     title = {Transformations which preserve harmonic coordinates},
     journal = {Doklady Akademii Nauk},
     pages = {1050--1053},
     year = {1968},
     volume = {181},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1968_181_5_a5/}
}