@article{ZVMMF_1987_27_12_a3,
     author = {A. S. Bratus' and A. D. Myshkis},
     title = {The conditions for an extremum in spectral isoperimetric problems with variable boundary},
     journal = {\v{Z}urnal vy\v{c}islitelʹnoj matematiki i matemati\v{c}eskoj fiziki},
     pages = {1790--1801},
     publisher = {mathdoc},
     volume = {27},
     number = {12},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZVMMF_1987_27_12_a3/}
}