Air Mail Proof 1951-57 Air 6c., 10c., 15c. and 25c. imperforate proof of each on printer's cards (3), each endorsed "Approved", one with a request for possible improvement, dated "10/10/51", "16/10/51" and "2/10/51" respectively; also 1957 Air 4c. imperforate proof on slightly soiled card, stamped and endorsed with approval, dated "21 Feb. 57"; five proofs in all