  The Turan bound is a famous result in graph theory, which relates the
independence number of an undirected graph to its edge density. Also the
Caro-Wei inequality, which gives a more refined bound in terms of the vertex
degree sequence of a graph, might be regarded today as a classical result. We
show how these statements can be generalized to directed graphs, thus yielding
a bound on directed feedback vertex number in terms of vertex outdegrees and in
terms of average outdegree, respectively.
