Klein bottle is a conceptual model in the field of mathematics, a non-directional plane with no distinction between "inside" and "outside" Just like a two-dimensional plane, if it is divided into two equal halves, it is two Mobius belts. Because of the special structure, it is impossible to construct such a curved surface in three-dimensional space, but a model can be constructed, that is, the thin end of an open conical tube is stuffed into the thick end (consistent with the opening direction) and then sealed with each other.