@article{SF_1972__4_133906,
     author = {L.N. Shevrin},
     title = {The {Sverdlovsk} tetrad.},
     journal = {Semigroup forum},
     pages = {274--280},
     publisher = {mathdoc},
     volume = {4},
     year = {1972},
     url = {http://geodesic.mathdoc.fr/item/SF_1972__4_133906/}
}