The Kelmans-Seymour conjecture II: 2-vertices in K_4^- (Intermediate structure and finding TK_5)

Graph Theory Seminar
Wednesday, March 2, 2016 - 3:05pm
1 hour (actually 50 minutes)
Skiles 005
Math, GT
We use K_4^- to denote the graph obtained from K_4 by removing an edge,and use TK_5 to denote a subdivision of K_5. Let G be a 5-connected nonplanar graph and {x_1, x_2, y_1, y_2} \subseteq V (G) such that G[{x_1,x_2, y_1, y_2}] = K_4^- with y_1y_2 \in E(G). Let w_1,w_2,w_3 \in N(y_2)- {x_1,x_2} be distinct. We show that G contains a TK_5 in which y_2 is not a branch vertex, or G - y_2 contains K_4^-, or G has a special 5-separation, or G' := G - {y_2v : v \in {w_1,w_2,w_3, x_1, x_2}} contains TK_5.In this talk, we will obtain a substructure in G' and several additional paths in G', and then use this substructure to find the desired TK_5.