@article{MZ_1995__218_4_174715,
     author = {Vesselin Petkov and Gregori Popov},
     title = {On the {Lebesgue} measure of the periodic points of a contact mainfold.},
     journal = {Mathematische Zeitschrift},
     pages = {91--102},
     publisher = {mathdoc},
     volume = {218},
     number = {4},
     year = {1995},
     zbl = {0816.58008},
     url = {http://geodesic.mathdoc.fr/item/MZ_1995__218_4_174715/}
}