@article{GDZPPN00231925X, title = {The Relative Spectrum of Elements in a Real Banach Algebra.}, journal = {Mathematische Annalen}, volume = {250}, year = {1980}, pages = {113-134}, zbl = {0421.46042}, url = {http://dml.mathdoc.fr/item/GDZPPN00231925X} }
Hile, G.N.; Pfaffenberger, W.E. The Relative Spectrum of Elements in a Real Banach Algebra.. Mathematische Annalen, Tome 250 (1980) pp. 113-134. http://gdmltest.u-ga.fr/item/GDZPPN00231925X/