@article{VMUMM_1991_4_a10,
     author = {A. B. Ugol'nikov},
     title = {Depth of formulas in some classes of $k$-valued logic},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {44--47},
     publisher = {mathdoc},
     number = {4},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1991_4_a10/}
}