@article{GDZPPN002207737,
title = {Bifurcation into gaps in the essential spectrum.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {405},
year = {1990},
pages = {1-34},
zbl = {0697.47063},
url = {http://dml.mathdoc.fr/item/GDZPPN002207737}
}
Stuart, Charles A.; Küpper, T. Bifurcation into gaps in the essential spectrum.. Journal für die reine und angewandte Mathematik, Tome 405 (1990) pp. 1-34. http://gdmltest.u-ga.fr/item/GDZPPN002207737/