Three color theorem and Four color theorem

According to the arrangement order of the vertexes in the line, the two-color theorem is derived. Add auxiliary lines to the vertexes that do not conform to the four-color closed chain, the one-color theorem and the two-color theorem,the coloring order of each vertex is locked, and the three-color theorem is derived. According to the one-color theorem, the two-color theorem, the three-color theorem and the law of chain structure, the four-color theorem is derived.