#### Title

Excluding a large theta graph

#### Document Type

Article

#### Publication Date

9-1-2018

#### Abstract

A theta graph, denoted θa,b,c, is a graph of order a+b+c−1 consisting of a pair of vertices and three internally-disjoint paths between them of lengths a, b, and c. In this paper we study graphs that do not contain a large θa,b,c minor. More specifically, we describe the structure of θ1,2,t-, θ2,2,t-, θ1,t,t-, θ2,t,t-, and θt,t,t-free graphs where t is large. The main result is a characterization of θt,t,t-free graphs for large t. The 3-connected θt,t,t-free graphs are formed by 3-summing graphs without a long path to certain planar graphs. The 2-connected θt,t,t-free graphs are then built up in a similar fashion by 2- and 3-sums. This result implies a well-known theorem of Robertson and Chakravarti on graphs that do not have a bond containing three specified edges.

#### Publication Source (Journal or Book title)

Journal of Combinatorial Theory. Series B

#### First Page

47

#### Last Page

79

#### Recommended Citation

Ding, G., & Marshall, E.
(2018). Excluding a large theta graph.* Journal of Combinatorial Theory. Series B**, 132*, 47-79.
https://doi.org/10.1016/j.jctb.2018.03.002