@article{1077313575,
author = {Beem, John K. and Ehrlich, Paul E.},
title = {A Morse index theorem for null geodesics},
journal = {Duke Math. J.},
volume = {46},
number = {1},
year = {1979},
pages = { 561-569},
language = {en},
url = {http://dml.mathdoc.fr/item/1077313575}
}
Beem, John K.; Ehrlich, Paul E. A Morse index theorem for null geodesics. Duke Math. J., Tome 46 (1979) no. 1, pp. 561-569. http://gdmltest.u-ga.fr/item/1077313575/