The three-day exhibition is displaying copies of documents written in Han (classical Chinese), Nom (Vietnamese ideographic script), Vietnamese and French, which were issued under the Vietnamese feudal dynasties and French administration in Indochina from the 17th century to the early 20th century.They show the process Vietnam continuously exercised and protected its sovereignty over Hoang Sa and Truong Sa islands.The Ha Tinh Department of Information and Communications said there will be more exhibitions of this kind to be held across the province.