@article{702252,
     title = {Necessary conditions for the multiple integral problem and elliptic variational inequalities},
     booktitle = {Equadiff 5},
     series = {GDML\_Books},
     publisher = {BSB B.G. Teubner Verlagsgesellschaft},
     address = {Leipzig},
     year = {1982},
     pages = {30-33},
     zbl = {0524.49014},
     url = {http://dml.mathdoc.fr/item/702252}
}

Barbu, Viorel. Necessary conditions for the multiple integral problem and elliptic variational inequalities, dans Equadiff 5, GDML_Books,  (1982), pp. 30-33. http://gdmltest.u-ga.fr/item/702252/