KV) 1971 SWITZERLAND, COMMEMORATIVE COVER OF THE FIRST AUSTRIAN AIRLINES / SWISSAIR JET CARAVELLE FLIGHT ON THE GRAZ–SALZBURG–ZURICH ROUTE OF 1 SEPTEMBER 1971, WITH AN AUSTRIAN 4 SCHILLING “INTERNATIONALES” STAMP AND A SPECIAL GRAZ POSTMARK OF 2.9.1971. ON THE REVERSE, ARRIVAL POSTMARK ZURICH 2.9.1971