umgebung(in de). Hotel Friederichs Duisburg. Retrieved on 2011-09-15. Name on the imprint page, no license
2011-09-15: E-mail sent
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Please specify if terms of license are complied with! Hydraulic Steel Industry(in en). KettenWulf Betriebs GmbH. Retrieved on 2011-09-16. No name, no license