The basic concept of fixed point theory is that for a function f(x), if there is an x that makes f(x)=x, then this x is called the fixed point of f(x). In this magic, the most critical step is to find this fixed point.
The magician first divided 2 1 card into three stacks, and then asked the audience to choose a stack and move it to the middle. Then, the magician repeats this process until all the cards are moved to the middle. Finally, the magician divided all the cards into three stacks, each with seven cards, and then repeated the process again, but this time he didn't show the audience the stack of cards he chose every time.
In this magic trick, the role of the fixed point is that even if all the cards are moved to the middle, the position of the middle stack of cards remains the same, that is, the fixed point. The key of this magic trick is to find the fixed point, and the magician can't detect the existence of the fixed point by repeating the same action.
So the calculation principle of 2 1 poker magic is the fixed point theory.