@article{TM_2011_274_a15,
     author = {A. L. Semenov and S. F. Soprunov},
     title = {Finite quantifier hierarchies in relational algebras},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {291--296},
     publisher = {mathdoc},
     volume = {274},
     year = {2011},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_2011_274_a15/}
}