@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/