@article{MOMA_1981__92_178040,
     author = {Wilfried Hauenschild and Jean Ludwig},
     title = {The {Injection} and the {Protection} {Theorem} for {Spectral} {Sets}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {167--178},
     publisher = {mathdoc},
     volume = {92},
     year = {1981},
     zbl = {0458.43009},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1981__92_178040/}
}