@article{SIGMA_2017_13_a33,
     author = {Sergey Ya. Startsev},
     title = {Formal {Integrals} and {Noether} {Operators} of {Nonlinear} {Hyperbolic} {Partial} {Differential} {Systems} {Admitting} a {Rich} {Set} of {Symmetries}},
     journal = {Symmetry, integrability and geometry: methods and applications},
     year = {2017},
     volume = {13},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SIGMA_2017_13_a33/}
}