@article{ZNSL_1992_203_a9,
     author = {Ya. V. Kurylev},
     title = {On the {Holmgren{\textendash}John} uniqueness theorem for the wave equation with piecewise analytic coefficients},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {113--136},
     year = {1992},
     volume = {203},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1992_203_a9/}
}