@article{1250129196, author = {Protter, M.H.}, title = {The generalized spectrum of second order elliptic systems}, journal = {Rocky Mountain J. Math.}, volume = {9}, number = {4}, year = {1979}, pages = { 503-518}, language = {en}, url = {http://dml.mathdoc.fr/item/1250129196} }
Protter, M.H. The generalized spectrum of second order elliptic systems. Rocky Mountain J. Math., Tome 9 (1979) no. 4, pp. 503-518. http://gdmltest.u-ga.fr/item/1250129196/