@article{SM_1977_33_3_a5,
     author = {V. F. Butuzov},
     title = {The angular boundary layer in mixed singularly perturbed problems for hyperbolic equations},
     journal = {Sbornik. Mathematics},
     pages = {403--425},
     publisher = {mathdoc},
     volume = {33},
     number = {3},
     year = {1977},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1977_33_3_a5/}
}