@article{SM_1980_37_2_a3,
     author = {N. Kh. Ibragimov},
     title = {On the theory of {Lie{\textendash}B\"acklund} transformation groups},
     journal = {Sbornik. Mathematics},
     pages = {205--226},
     year = {1980},
     volume = {37},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1980_37_2_a3/}
}