# Neil Robertson

# Minor relations for directed graphs

## Abstract for the Special Combinatorics Seminar

Friday, April 23, 1999

The beginning of a general theory of digraph minors is struggling to
appear. What are the primary inclusion relations? What structure
theory reflects tree-width and universal surface structure? Where does
well-quasi-ordering come into the picture? Are there interesting
algorithmical decision problems that are not NP hard? Is there any
prospect of a coherent body of theorems central to directed graphs?
Some formal and informal reflections on these questions (representing
the graph minor people) will be the subject matter of this talk.