How Tian Zige occupied the case of addition and subtraction
1, addition: the plus sign is written in the middle of Tian Zige, and the sum of the two addends is written in the left position in the middle of the right half of Tian Zige.
2. Subtraction: The minuend is written in the upper left corner of Tian Zige, the minuend is written in the upper right corner of Tian Zige, and the divisor is written in the middle left position of the right half of Tian Zige.