@article{GDZPPN00202599X,
title = {A Geometrical Theory of Multiple Integral Problems in the Calculus of Variations},
journal = {Aequationes mathematicae},
volume = {7},
year = {1971},
pages = {173-181},
zbl = {0232.49010},
url = {http://dml.mathdoc.fr/item/GDZPPN00202599X}
}
DAVIES, E.T. A Geometrical Theory of Multiple Integral Problems in the Calculus of Variations. Aequationes mathematicae, Tome 7 (1971) pp. 173-181. http://gdmltest.u-ga.fr/item/GDZPPN00202599X/