Click image, no promises.
The stamp is Real, not Faux. Dedekind lives Forever, the Equation is True, but alas the postal issuing authority, DDR, Deutsche Demokratische Republik -- East Germany -- has vanished.
This was a very smart guy. He studied at Göttingen, Berlin, and taught at the Polytechnic in Zurich, and in his native Braunschweig / Brunswick.