@article{MAN_1971__192_162147,
     author = {Bernhard GRAMSCH and David LAY},
     title = {Spectral {Mapping} {Theorems} for {Essential} {Spectra.}},
     journal = {Mathematische Annalen},
     pages = {17--32},
     publisher = {mathdoc},
     volume = {192},
     year = {1971},
     zbl = {0203.45601},
     url = {http://geodesic.mathdoc.fr/item/MAN_1971__192_162147/}
}