@article{ZNSL_1967_4_a16,
     author = {V. P. Orevkov},
     title = {Unsolvability in the modal predicate calculus of the class of formulas containing only one monadic predicate variable},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {168--173},
     publisher = {mathdoc},
     volume = {4},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1967_4_a16/}
}