ON THE PLANAR IMBEDDING OF LINEAR GRAPHS(CONTINUED)
线性图的平面嵌入问题（续）

5.FURTHER REDUCTION OF FUNDAMENTAL SYSTEM OF LINEAR EQUATIONSThe fundamental system of linear equations(If)in preceding Sect 4 can actuallybe put in a much simpler form.For this purpose let us denote by NT a certain neigh-borhood of T in G sufficiently small so that the T-immersions considered will be someimbeddings when restricted on NT and that all possible intersections of images of dis-joint external edges are not in NT.We shall call these T-immersions also NT-immer-sions.