AUXILIARY GRAPHS OF PROJECTIVE PLANAR SIGNED GRAPHS
射影平面上标号图的辅助图

The planarity auxiliary graph of a graph is given by Yanpei Liu. This paper generalizes the planarity auxiliary graph to projective planar. The projective planarity of signed graphs is characterized as follows: the corresponding auxiliary graph of a given signed graph $G$ is balanced iff the graph $G$ is projective planar.