Line digraphs and coreflexive vertex sets
  The concept of coreflexive set is introduced to study the structure of digraphs. New characterizations of line digraphs and nth-order line digraphs are given. Coreflexive sets also lead to another natural way of forming an intersection digraph from a given digraph. 
Xinming Liu (Tianjin University) and Douglas B. West (University of   Illinois)