@article{DAN_1978_240_3_a12,
     author = {V. B. Shehtman},
     title = {An undecidable superintuitionistic propositional calculus},
     journal = {Doklady Akademii Nauk},
     pages = {549--552},
     publisher = {mathdoc},
     volume = {240},
     number = {3},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1978_240_3_a12/}
}