@article{AL_1993_32_1_a3,
     author = {Yu. G. Ventsov},
     title = {Effective selection operations on constructive and positive
},
     journal = {Algebra i logika},
     pages = {45--53},
     publisher = {mathdoc},
     volume = {32},
     number = {1},
     year = {1993},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1993_32_1_a3/}
}