@article{SEMR_2010_7_a39,
     author = {N. A. Lyul'ko},
     title = {The increasing smoothness property of solutions to some hyperbolic problems in two independent variables},
     journal = {Sibirskie \`elektronnye matemati\v{c}eskie izvesti\^a},
     pages = {413--424},
     year = {2010},
     volume = {7},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SEMR_2010_7_a39/}
}