@article{AL_2004_43_4_a4,
     author = {A. I. Stukachev},
     title = {$\Sigma${-Definability} in {Hereditarily} {Finite} {Superstructures} and {Pairs} of {Models}},
     journal = {Algebra i logika},
     pages = {459--481},
     publisher = {mathdoc},
     volume = {43},
     number = {4},
     year = {2004},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_2004_43_4_a4/}
}