@article{ZNSL_1993_208_a6,
     author = {N. Yu. Netsvetaev},
     title = {An analogue of the {Maslov} index},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {133--135},
     publisher = {mathdoc},
     volume = {208},
     year = {1993},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1993_208_a6/}
}