@article{MS2_1978__43_166629,
     author = {Kristi Mattila},
     title = {On proper boundary points of the spectrum and complemented eigenspaces.},
     journal = {Mathematica Scandinavica},
     pages = {363--368},
     year = {1978},
     volume = {43},
     zbl = {0387.47001},
     url = {http://geodesic.mathdoc.fr/item/MS2_1978__43_166629/}
}