@article{TM_1991_200_a3,
     author = {V. A. Baikov and R. K. Gazizov and N. Kh. Ibragimov},
     title = {Approximate symmetries and preservation laws},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {35--45},
     publisher = {mathdoc},
     volume = {200},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1991_200_a3/}
}