10 Pfg. on 20 Pfg. Prussian-blue unperforated in the horizontal gutter pair with the overprint combination "Ia / ZIIa" (field 15 and 16) in perfect unhinged mint in outstanding quality with appropriate certificate with photograph Gruber BPP, extremely scarce variety, the so far lacking offer not calculated is - a rarity for the large Upper Silesia collection!