@article{SM_1977_31_2_a10,
     author = {A. I. Citkin},
     title = {On admissible rules of intuitionistic propositional logic},
     journal = {Sbornik. Mathematics},
     pages = {279--288},
     year = {1977},
     volume = {31},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1977_31_2_a10/}
}