@article{MZM_1969_6_6_a2,
     author = {Yu. I. Yanov},
     title = {On directed transformations of formulas},
     journal = {Matemati\v{c}eskie zametki},
     pages = {663--668},
     publisher = {mathdoc},
     volume = {6},
     number = {6},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1969_6_6_a2/}
}