@article{GDZPPN00247221X, title = {Maximum Principles and Duality.}, journal = {Monatshefte f\"ur Mathematik}, volume = {62}, year = {1958}, pages = {56-75}, zbl = {0094.29901}, url = {http://dml.mathdoc.fr/item/GDZPPN00247221X} }
Redheffer, Raymond M. Maximum Principles and Duality.. Monatshefte für Mathematik, Tome 62 (1958) pp. 56-75. http://gdmltest.u-ga.fr/item/GDZPPN00247221X/