Pam shows Creed two pictures and claims that they are different, but Creed cannot see any difference between them. Pam wants to convince Creed that they really are different, but without revealing what the difference is. How can Creed test Pam so that if the pictures really are different, Pam will pass the test while revealing nothing more than this fact to Creed; and if the pictures are identical, Pam will fail the test with probability at least 99%? (Just describe