@article{TM_2011_274_a19,
     author = {V. B. Shehtman},
     title = {On squares of modal logics with additional connectives},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {343--351},
     publisher = {mathdoc},
     volume = {274},
     year = {2011},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_2011_274_a19/}
}