CH 1938 B3-B6 Pro Patria FDC ill with address

Switzerland 1940 B (Swiss National Fête and PRO PATRIA - issues)
Historical motives, SBK B3-B6, Michel 364-367,
FDC illustrated envelope (Format C6) with address, cancelled "20.III.40 Zürich 32 - Seebach", transported to USA, Hintermann letter,
in very good condition, very decorative, Certificate Liniger.