1935, 10 C. airmail, overprint dull, block of four in mixed franking with 20 C. airmail green on properly franked home letter to the 1. winter airmail in the Buendner alps, flown Zurich - St. Moritz - Zurich, very fine. (Zumstein No. F19 b, F4.1.09 s Fr. for lots nice 480.-)