@article{ZNSL_1987_163_a14,
     author = {D. R. Yafaev},
     title = {Eikonal approximation for fast-decreasing {potentials.~I}},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {166--185},
     year = {1987},
     volume = {163},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1987_163_a14/}
}