@article{TM_1976_142_a17,
     author = {S. S. Ryshkov},
     title = {On the problem of determining perfect quadratic forms of several variables},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {215--239},
     publisher = {mathdoc},
     volume = {142},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1976_142_a17/}
}