Matthew Bunn, a nuclear expert at the Belfer Center at Harvard University, said in a interview on Monday that the Obama administration had some latitude in defining what constitutes “suspension” of nuclear work.One possibility, he said, was “what you call warm shutdown,” in which the centrifuges keep spinning, but not producing new enriched uranium, akin to leaving a car running, but in park. That would allow both sides to claim victory: the Iranians could claim they had resisted American efforts to shut down the program, while the Americans and Europeans could declare that they had halted the stockpiling of material that could be used to produce weapons.