三次图的收缩及其迭线图的分类

The Contraction of the Cubic Graph and the Classification of Iterated Line Graph

设图G为含有三角形或四边形的三次图,G_△为G的二角形收缩;G_□为G的四边形收缩。本文用计算机辅助证明了,若L(G)是2类的,则L(G_□)是2类的,若L^2(G)为2类的,则L^2(G_△)或L^2(G_□)为2类的。

Suppose G is a cubic graph which contains the triangles or quadrilaterals,G_Δ is a trian-gle-contract of the graph G; is a qudrilateral-contract of the graph G, With computer as-sist the paper proves that: lf L (G) is of clas. 2, the L(G_□) is of class 2; if L^2(G) is ofclass 2. the L^2 (G_△) or L^2 (G_□) is of class 2.