@article{ZNSL_1991_195_a1,
     author = {V. M. Babich},
     title = {Absence of singularities of {Gaussian} beams in diffusion equation case},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {14--18},
     publisher = {mathdoc},
     volume = {195},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1991_195_a1/}
}