CuA refers to the complement set of A, and the complement set of A refers to removing all elements of A within the scope of a complete set. Then the translation of set A and CuA is the set of elements in set A plus all elements of the complete set, so it is still a complete set.

2.P|PA=PB} indicates the middle vertical line of the line segment AB, because AB is a fixed point, PA = Pb, and the points on the middle vertical line satisfy.

{P|PO= 1} represents a circle with o as the center and a radius of 1.

3. Intersection is to take the same parts of them. To unite is to put all their elements together.

4. Are cubs really included in the CuA?

Because a is really included in b, it means that the scope of a is relatively small and the scope of b is relatively large. However, the complete works are affirmative.

CuA means hollowing out the rest of Part A in the complete works. Then CuA naturally digs less and CuB digs more. So CuB is really included in CuA.