The existence of even factors in iterated line graphs

An even factor of a graph is a spanning subgraph of image in which all degrees are even, positive integers. In this paper, we characterize the claw-free graphs having even factors and then prove that the image-iterated line graph image of image has an even factor if and only if every end branch of image has length at most image and every odd branch-bond of image has a branch of length at most image.