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                * Princeton Discrete Math Seminar *
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Date: Thursday 12th November, 3:00 in Fine Hall 224.
 
Speaker: Emily Marshall (Louisiana State)

Title: Excluding theta graphs

Abstract: A theta graph, denoted T(a,b,c), consists of a pair of  
vertices together with three disjoint paths between the vertices of  
lengths a, b, and c. In this talk, we characterize graphs which  
exclude certain theta graphs as a minor. We begin with small theta  
graphs, in particular those with at most 7 edges. This work is part of  
a larger project which characterizes H-minor-free graphs for all  
2-connected graphs H on at most 7 edges and is joint with Mark  
Ellingham, Tom McCourt, and Tony Nixon. Next we look at excluding  
large theta graphs. We allow at least one of the paths to be  
arbitrarily long. The most complicated case is excluding T(t,t,t)  
where t is any large integer. The work on large theta graphs is joint  
with Guoli Ding.

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Next week: Federico Ardila

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