Pavol Hell (Simon Fraser University): 2-Directional Ray Graphs, Extension Theorems, and a Dichotomy for Signed Graphs

2-directional ray graphs are an interesting graph class sitting between interval bigraphs and chordal bipartite graphs; they play an important role in the dichotomy of list homomorphism problems. I will discuss a new characterization and extension theorem for 2-directional ray graphs, as well as its analogue for the class of interval graphs. As an application, I will deduce a dichotomy of list homomorphisms for signed graphs in an important special case, proving a conjecture of Kim and Siggers. This is joint work with Jan Bok, Rick Brewster, Nikola Jedlickova, and Arash Rafiey.


Zoom:
https://zoom.us/j/2961946869