A French prime minister who had just lost power backdated his signature on a 1957 document that committed his country to aiding Israel's construction of a nuclear reactor, a new book about Shimon Peres says. Some experts say the move helped Israel acquire atomic weapons. "Shimon Peres: The Biography" also says an earlier, secret agreement between the two nations pledged French cooperation on Israeli research and development of nuclear weapons, even before the French government formally decided to build its own atomic bombs. The two nations agreed in 1961 to end the cooperation agreements, but France helped Israel finish work on the Dimona nuclear facility in the Negev Desert. Peres persuaded Bourges-Maunoury to sign the cooperation pact on Oct. 1, 1957, a day after the French prime minister's government collapsed, but to date the document the previous day, Sept. 30, the book says. It says Peres knew the new French government wouldn't be as friendly to Israel.