@article{AL_1966_5_4_a2,
     author = {Yu. I. Merzlyakov},
     title = {Positive formulae on free groups},
     journal = {Algebra i logika},
     pages = {25--42},
     publisher = {mathdoc},
     volume = {5},
     number = {4},
     year = {1966},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1966_5_4_a2/}
}