Planar Graph Theory and the Four Color Problem (Ⅳ) -Three Colorings and Geometric theory of the Four Color Problem

Abstract:

      This is the fourth part of the series of five papers about planar graph theory and the four color problem.It contains the following five sections. §16 Three color problems;§17 The Tait coloring of edges, §18 The four color problem and chain groups; §19 Proje-ctive geometry and the four color problem; §20 On the number of four colorings.