Space is the measure of the universe, which is divided into many dimensions, namely zero-dimensional point, one-dimensional line, two-dimensional plane, three-dimensional body and so on. Among them, the former dimension is composed of the latter dimension, such as points forming lines. That is, multidimensional space contains low dimensions. At present, people have not reached a conclusion on the dimension of the universe, and it is generally believed that time similar to space is the external manifestation of the movement and change of the universe. A collection is to group things together according to specific attributes. The referenced property must be. For example, a higher class of people is not a collection. One dimension of the interval is the selected line segment on the number axis, the other dimension is the region, and so on. Neighborhood is a length defined with reference to a point and is symmetrical with the point.