1938, 50 C. Airmail issue \"PRO aero\", horizontal pair from left margin of sheet, mint never hinged, faultless condition, very rare stamp, expertized Weid and photo expertize A von der Weid SBPV as well photo expertize Jean Claude Marchand SBPV (2023) \"in perfect condition. \", Michel 28.000.- - already mint never hinged single pieces of this stamp are large rarities, a horizontal pair places an extraordinary rarity of Switzerland, but also the world-wide airmail issues dar!