@article{ZNSL_2015_438_a13,
     author = {M. M. Popov},
     title = {On the {Morse} index calculation and the prolongation of the ray formulae beyond caustics},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {225--235},
     publisher = {mathdoc},
     volume = {438},
     year = {2015},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2015_438_a13/}
}