@article{MAT_1972_16_1_a2,
     author = {R. Sakamoto},
     title = {Mixed problems for hyperbolic equations. {I.~Energy} inequalities},
     journal = {Matematika},
     pages = {62--80},
     publisher = {mathdoc},
     volume = {16},
     number = {1},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MAT_1972_16_1_a2/}
}