@article{MZM_1975_17_1_a10,
     author = {V. A. Il'in},
     title = {Proof of uniqueness and membership in $W^1_2$ of the classical solution of a mixed problem for a self-adjoint hyperbolic equation},
     journal = {Matemati\v{c}eskie zametki},
     pages = {91--101},
     publisher = {mathdoc},
     volume = {17},
     number = {1},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1975_17_1_a10/}
}