@article{MZM_1993_53_3_a2,
     author = {A. N. Degtev},
     title = {Some properties of deducibility operators},
     journal = {Matemati\v{c}eskie zametki},
     pages = {23--28},
     publisher = {mathdoc},
     volume = {53},
     number = {3},
     year = {1993},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1993_53_3_a2/}
}