@article{IM2_1968_2_4_a9,
     author = {V. A. Yankov},
     title = {Three sequences of formulas with two variables in the positive propositional logic},
     journal = {Izvestiya. Mathematics },
     pages = {845--848},
     publisher = {mathdoc},
     volume = {2},
     number = {4},
     year = {1968},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1968_2_4_a9/}
}