1935, 10 C. airmail, matte overprint, block of four in a mixed franking with 20 C. green airmail on a properly franked inland letter for the 1st winter airmail in the Grison Alps, flown Zurich - St. Moritz - Zurich, excellent condition. (Zumstein No. F19 b, F4. 1. 09 s Fr for loose already 480.-)