@article{AL_1998_37_3_a6,
     author = {S. I. Mardaev},
     title = {Negative modal schemes},
     journal = {Algebra i logika},
     pages = {329--337},
     publisher = {mathdoc},
     volume = {37},
     number = {3},
     year = {1998},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1998_37_3_a6/}
}