@article{1183419223, author = {Mason, Max}, title = {A necessary condition for an extremum of a double integral}, journal = {Bull. Amer. Math. Soc.}, volume = {14}, number = {3}, year = {1907}, pages = { 293-298}, language = {en}, url = {http://dml.mathdoc.fr/item/1183419223} }
Mason, Max. A necessary condition for an extremum of a double integral. Bull. Amer. Math. Soc., Tome 14 (1907) no. 3, pp. 293-298. http://gdmltest.u-ga.fr/item/1183419223/