@article{ZNSL_1989_179_a2,
     author = {R. F. Bikbaev},
     title = {On non-linear diffraction in defocusing medium},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {23--31},
     year = {1989},
     volume = {179},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1989_179_a2/}
}