@article{AL_1999_38_5_a3,
     author = {S. I. Mardaev},
     title = {Modal positive operators},
     journal = {Algebra i logika},
     pages = {585--597},
     year = {1999},
     volume = {38},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1999_38_5_a3/}
}