@article{AM2_1980__21_182431,
     author = {Thomas G. Berry and Sarel Venter},
     title = {Integral formulae associated with non-parameter invariant multiple integral problems of arbitrary order in the calculus of variations.},
     journal = {Aequationes mathematicae},
     pages = {200--224},
     publisher = {mathdoc},
     volume = {21},
     year = {1980},
     zbl = {0459.49032},
     url = {http://geodesic.mathdoc.fr/item/AM2_1980__21_182431/}
}