"ZAHLENSPIEGEL 2012" [STATISTICS 2012] (PDF) (به آلمانی). vgF. December 31, 2012. Archived from the original(PDF) on 21 October 2013. Retrieved 2013-09-29.
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"ZAHLENSPIEGEL 2012" [STATISTICS 2012] (PDF) (به آلمانی). vgF. December 31, 2012. Archived from the original(PDF) on 21 October 2013. Retrieved 2013-09-29.