A high school textbook that is almost 30 years old proves Cambodian land was lost to Vietnam under Prime Minister Hun Sen, Cambodia Watchdog Council Rong Chhun claimed yesterday. The book, used to teach seventh-graders geography under Hun Sen’s Ministry of Education in 1985, says the island of Koh Tral belonged to Cambodia at the time, Chhun said. Hun Sen has long held that Cambodia lost the land to Vietnam in the 1960s under King Norodom Sihanouk’s rule. The premier last week said that members of the opposition party who say they will seek repatriation of the land from Vietnam could provoke a war. Not impressed by the book Chhun found, minister in charge of border affairs, Va Kimhong, said the land was, indeed, lost before Hun Sen came to power.