@article{ZNSL_2006_339_a8,
     author = {N. V. Smorodina},
     title = {The invariant and
},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {135--150},
     publisher = {mathdoc},
     volume = {339},
     year = {2006},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2006_339_a8/}
}