Extremal Functions for Graph Linkages and Rooted Minors

Extremal functions for rooted minors

The graph G contains a graph H as a minor if there exist pair-wise disjoint sets {Si ⊆ V (G)|i = 1, . . . , |V (H)|} such that for every i, G[Si] is a connected subgraph and for every edge uv in H, there exists an edge of G with one end in Su and the other end in Sv. A rooted H minor in G is a minor where each Si of minor contains a predetermined xi ∈ V (G). We prove that if the constant c is s...

Interval minors of complete bipartite graphs

Interval minors of bipartite graphs were recently introduced by Jacob Fox in the study of Stanley-Wilf limits. We investigate the maximum number of edges in Kr,s-interval minor free bipartite graphs. We determine exact values when r = 2 and describe the extremal graphs. For r = 3, lower and upper bounds are given and the structure of K3,s-interval minor free graphs is studied.

The Extremal Functions for Triangle-free Graphs with Excluded Minors

We prove two results: 1. A graph G on at least seven vertices with a vertex v such that G − v is planar and t triangles satisfies |E(G)| ≤ 3|V (G)| − 9 + t/3. 2. For p = 2, 3, . . . , 9, a triangle-free graph G on at least 2p − 5 vertices with no Kp-minor satisfies |E(G)| ≤ (p− 2)|V (G)| − (p− 2).

Graph Minors

For a given graph G and integers b, f ≥ 0, let S be a subset of vertices of G of size b + 1 such that the subgraph of G induced by S is connected and S can be separated from other vertices of G by removing f vertices. We prove that every graph on n vertices contains at most n/ b+f b such vertex subsets. This result from extremal combinatorics appears to be very useful in the design of several e...

B . A . Reed Graph Minors I : Rooted Routing