@article{1077490488, author = {Morse, Marston}, title = {The index theorem in the calculus of variations}, journal = {Duke Math. J.}, volume = {4}, number = {1}, year = {1938}, pages = { 231-246}, language = {en}, url = {http://dml.mathdoc.fr/item/1077490488} }
Morse, Marston. The index theorem in the calculus of variations. Duke Math. J., Tome 4 (1938) no. 1, pp. 231-246. http://gdmltest.u-ga.fr/item/1077490488/