@article{UZKU_1969_129_4_a2,
     author = {N. K. Zamov and V. I. Sharonov},
     title = {The strengthening of formulae that are provable in propositional calculus},
     journal = {U\v{c}\"enye zapiski Kazanskogo universiteta. Seri\^a Fiziko-matemati\v{c}eskie nauki},
     pages = {21--31},
     publisher = {mathdoc},
     volume = {129},
     number = {4},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/UZKU_1969_129_4_a2/}
}