Oh, not specifically and officially; I don't know what actual contractual or legal rules surround this, and it could well be that trading is contingent on a con

Oh, not specifically and officially; I don't know what actual contractual or legal rules surround this, and it could well be that trading is contingent on a contract that allows them to do whatever they want. By "rules", I mean the usual rules that people believe are in force, like "Once I buy or sell, it stays bought or sold". In exceptional situations (like this one, or 9/11), it always seems to turn out that honoring obligations was optional all along, doesn't it?