@article{DE_1990_26_7_a2,
     author = {E. S. Pyatnitskii and L. B. Rapoport},
     title = {A method for constructing invariant functions and the study of phase portraits of dynamical systems on a computer},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1116--1126},
     publisher = {mathdoc},
     volume = {26},
     number = {7},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1990_26_7_a2/}
}