@article{1102947732, author = {Showalter, R. E.}, title = {Equations with operators forming a right angle.}, journal = {Pacific J. Math.}, volume = {49}, number = {2}, year = {1973}, pages = { 357-362}, language = {en}, url = {http://dml.mathdoc.fr/item/1102947732} }
Showalter, R. E. Equations with operators forming a right angle.. Pacific J. Math., Tome 49 (1973) no. 2, pp. 357-362. http://gdmltest.u-ga.fr/item/1102947732/