@article{MZM_1987_41_1_a8,
     author = {A. E. Andreev},
     title = {The complexity of the realization of subdefinite matrices by gate schemes},
     journal = {Matemati\v{c}eskie zametki},
     pages = {77--86},
     year = {1987},
     volume = {41},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1987_41_1_a8/}
}