Firstly, it is clear that some elements in the set are numbers, such as {1, 2, 3, 4}, and some are points, such as {( 1, 2), (3, 4)}, which cannot be confused; And some may be represented by different letters, but they are actually the same, for example, {x|x= 1} and {y|y= 1} are the same;

Then there is the intersection of sets, sum, complement, a number, which should be very simple, such as {1, 2,3,4} and {2,3,4,5}, and; If it is a range, such as {x | x >；; 2} and {x | x