@article{DAN_1963_148_4_a7,
     author = {V. A. Matulis},
     title = {Variants of the classical predicate calculus with a unique tree of deduction},
     journal = {Doklady Akademii Nauk},
     pages = {768--770},
     publisher = {mathdoc},
     volume = {148},
     number = {4},
     year = {1963},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1963_148_4_a7/}
}