50 Kopeks black on dark grey-blue, imperforate, horizontal pair with stamps types I and VII, sheet positions 8/9 with complete "Probendruck" (proof) overprint, unused without gum as issued, right stamp from position 9 with setting error VII, occurring only once per sheet; left stamp from position 8, type I, has a print run of 15 examples, thus the horizontal pair is unique and among the greatest rarities of the German occupation issues of World War II, signed Z. Mikulski, photo certificate Walter Zirath BPP "The condition is faultless.", Mi. 36.000.-