Hochschularchiv RWTH Aachen Nr. 10114, Bl. 18: Matrikel 1870/71 Bl. 18
<a href="https://en.wikipedia.org/wiki/de:User:Historiograf" class="extiw" title="w:de:User:Historiograf">Klaus Graf</a>
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selbst fotografiert (<a href="https://en.wikipedia.org/wiki/de:User:Historiograf" class="extiw" title="w:de:User:Historiograf">Klaus Graf</a>)