每个直径不大于2的图的线图是泛圈的或4圈或5圈

The Line Graph of a Graph with Diameter at Most 2 Is Pancyclic or a Cycle of Length 4 or 5

图的直径是指图的顶点间的最大距离．该文证明了每个直径不大于２的图的线图是泛圈的或是４圈或５圈。

It is proved that the line graph of a graph with diameter at most 2 is pancyclic or a cycle of length 4 or 5.And the result is best possible.