@article{1077491419,
author = {Graves, Lawrence M.},
title = {The Weierstrass condition for multiple integral variation
problems},
journal = {Duke Math. J.},
volume = {5},
number = {1},
year = {1939},
pages = { 656-660},
language = {en},
url = {http://dml.mathdoc.fr/item/1077491419}
}
Graves, Lawrence M. The Weierstrass condition for multiple integral variation
problems. Duke Math. J., Tome 5 (1939) no. 1, pp. 656-660. http://gdmltest.u-ga.fr/item/1077491419/