@article{TMF_1998_116_2_a2,
     author = {V. S. Novikov},
     title = {Equations invariant under differential substitutions},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {193--200},
     publisher = {mathdoc},
     volume = {116},
     number = {2},
     year = {1998},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_1998_116_2_a2/}
}