Line-graphs of cubic graphs are normal

A graph is called normal if its vertex set can be covered by cliques Q(1), Q(2),...,Q(k) and also by stable sets S-1, S-2,..., S-l, such that S-i boolean AND Q(j) not equal empty set for every i, j. This notion is due to Korner, who introduced the class of normal graphs as an extension of the class of perfect graphs. Normality has also relevance in information theory. Here we prove, that the line graphs of cubic graphs are normal. (C) 2007 Elsevier B.V. All rights reserved.