@article{MZM_1981_29_6_a11,
     author = {A. U. Muravitskii},
     title = {Finite approximability of the~$I^\Delta$ calculus and the existence of an extension having no model},
     journal = {Matemati\v{c}eskie zametki},
     pages = {907--916},
     year = {1981},
     volume = {29},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1981_29_6_a11/}
}