Braces ({}) are sets, and the brackets () in the set include numerical ranges such as numbers, x, y, etc. ) is not used in the set, but it is used when describing the interval, indicating that the brackets in the closed interval are usually intersection, complement and union in the set, and used in the interval to indicate the open interval. Braces, such as {x | x >；; 3} (indicating that the value range of x is greater than three, or you can add a ","after the writing attribute, such as R real number, N natural number and Z integer). For example, 3,5 means that the range of an unknown number is 3-5, including 3 and 5 brackets. For example, (3,5) indicates that the range of an unknown number is 3-5, excluding.