@article{AL_2008_47_3_a3,
     author = {A. S. Morozov and M. V. Korovina},
     title = {$\Sigma${-Definability} of countable structures over real numbers, complex numbers, and quaternions},
     journal = {Algebra i logika},
     pages = {335--363},
     publisher = {mathdoc},
     volume = {47},
     number = {3},
     year = {2008},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_2008_47_3_a3/}
}