@article{ZNSL_1979_89_a1,
     author = {V. M. Babich},
     title = {The focussing problem and spectral function asymptotics of {Laplace{\textendash}} {Beltrami} {operator.~II}},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {14--53},
     year = {1979},
     volume = {89},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1979_89_a1/}
}