Let me give you an example: for example, the first line has 10 hand, that is, 5 buys and 5 sells at the same price. This should be easy to understand, right? Similarly, if you pay with one hand, you must sell with one hand, so the number of hands to be sold is always even.

If the above five orders are all open positions, and four of the five orders are open positions, and 1 order is open position, then ......

There will be no odd opening and even closing (and vice versa), because in that case, there will definitely be a single hand or a single hand without a corresponding reverse order, which is impossible.