@article{1077491575,
author = {Reid, William T.},
title = {The Jacobi condition for the double integral problem of the
calculus of variations},
journal = {Duke Math. J.},
volume = {5},
number = {1},
year = {1939},
pages = { 856-870},
language = {en},
url = {http://dml.mathdoc.fr/item/1077491575}
}
Reid, William T. The Jacobi condition for the double integral problem of the
calculus of variations. Duke Math. J., Tome 5 (1939) no. 1, pp. 856-870. http://gdmltest.u-ga.fr/item/1077491575/