@article{IM2_1970_4_5_a0,
     author = {M. M. Kipnis},
     title = {Invariant properties of systems of formulas of elementary axiomatic},
     journal = {Izvestiya. Mathematics},
     pages = {965--978},
     year = {1970},
     volume = {4},
     number = {5},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1970_4_5_a0/}
}