CH 1977 Stamp Day St-Imier BE, cover cancelled 3.12.77 2616 Renan (BE) Horse mail transport to St-Imier

Switzerland 1977 Stamp Day St-Imier BE,
official cover "Journée du Timbre - Giornata del Francobollo - Tag der Briefmarke - Di dalla Marca postala - Saint-Imier 1977 -
Carte officielle VSPHV / USFS / USPhS - Imier terrassant le Griffon",
Horse mail transport with Stagecoach from Renan via Sonviller to St-Imier
Black add-on bar cancellation "R.RENAN" and
blue impression "Transport par Diligence, Renan - Sonvillier - Saint-Imier"
with Pro Juventute stamps, without address, cancelled "3.12.77 2616 Renan (BE)",
backside arrival cancellation "3-4.12.77 2610 St-Imier - Journée du Timbre", luxury conservation.