Backhand is to flatten the original order, and then use the same number of hands as the original order to open and reverse the order. Reverse opening is to open a reverse order with the same number of hands as the original order without moving the original order. . . Backhand is a way to deny the original order and reverse the direction. . . . . Reverse opening, also known as locking, is a measure taken to prevent the risk from expanding, because the original order direction is not wrong, but it has not developed in the expected direction in the short term.