The existence of even factors in iterated line graphs

An even factor of a graph is a spanning subgraph of GG 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 nn-iterated line graph Ln(G)Ln(G) of GG has an even factor if and only if every end branch of GG has length at most nn and every odd branch-bond of GG has a branch of length at most n+1n+1.