@article{INTD_1989_34_a0,
     author = {I. Sh. Akhatov and R. K. Gazizov and N. Kh. Ibragimov},
     title = {Nonlocal symmetries. {Heuristic} approach},
     journal = {Itogi Nauki i Tekhniki. Seriya Sovremennye Problemy Matematiki. Noveishie Dostizheniya},
     pages = {3--83},
     publisher = {mathdoc},
     volume = {34},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/INTD_1989_34_a0/}
}