With waves and smiles, the leaders of North and South Korea met for a third summit. Even as the historic cooperation is on display, however, one question looms over this and other signs of progress on denuclearization: Is North Korea serious when it talks about giving up its nuclear weapons?

This week, South Korean President Moon Jae-in is in North Korea for a three-day summit with North Korean dictator Kim Jong Un. The subjects of their talks are familiar: formally ending the Korean war, progress on denuclearization, and, potentially, reunification of the divided peninsula.