@article{ZNSL_1979_88_a15,
     author = {S. V. Solov'ev},
     title = {Preservation of the equivalence of proofs under reduction of the formula depth},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {197--208},
     publisher = {mathdoc},
     volume = {88},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1979_88_a15/}
}