@article{MZM_1976_20_3_a9,
     author = {D. P. Skvortsov},
     title = {The occurrence of an implication in finitely valid, intuitively improvable formulas of propositional logic},
     journal = {Matemati\v{c}eskie zametki},
     pages = {383--390},
     publisher = {mathdoc},
     volume = {20},
     number = {3},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1976_20_3_a9/}
}