Air stamps

Quality: *

Group of 4 stamps of OBP n° PA16-Cu "50c on 1,50fr - Airmail Stamps 1936 issue", all with curiosity of surcharge: (1x) inverted, (1x) misplaced upwards, (2x) "A CHEVAL", mint and hinged, some rust, but very scarce, vf/f/to be checked