Unavoidable induced subgraphs forced by graphs with many vertices of prescribed properties
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arXiv
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866915653281120256 |
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| author | Sun, Jin Hou, Xinmin |
| author_facet | Sun, Jin Hou, Xinmin |
| contents | Given a function $p : V(G)\to \mathbb N$ and an integer $k\ge 0$, define $p_k(G)$ as the number of vertices with $p(v)\ge k$. We say that $p_k(G)$ is bounded for all $\HH$-free graphs if there exists a constant $c=c(\HH)$ such that $p_k(G)<c$ for all such graphs $G$. Here, a graph $G$ is said to be $\HH$-free if it contains no member of $\HH$ as an induced subgraph. When $p$ represents the degree of a vertex, Ramsey's theorem implies that $p_0(G)$ is bounded for every $\{K_n, E_n\}$-free graphs, where $K_n$ and $E_n$ denote the complete graph and the edgeless graph on $n$ vertices, respectively. The connected version of Ramsey's theorem says that $p_0(G)$ is bounded for all $\{K_n, P_n, K_{1,n}\}$-free connected graphs, where $P_n$ and $K_{1,n}$ are the $n$-vertex path and the star with $n$ leaves. In this paper, we extend the Ramsey's theorem to $p_2(G)$ where $p$ denotes the degree, the local independent number, the local component number, and sharp degree, that is, we characterize the forbidden family of graphs $\HH$ such that $p_2(G)$ is bounded for all (connected) $\HH$-free graphs. Moreover, we also characterize the forbidden family of graphs $\HH$ for which there is a constant $c=c(\HH)$ such that $p_c(G)$ is bounded for all $\HH$-free graphs. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_04414 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Unavoidable induced subgraphs forced by graphs with many vertices of prescribed properties Sun, Jin Hou, Xinmin Combinatorics 05C07, 05C55, 05C75 Given a function $p : V(G)\to \mathbb N$ and an integer $k\ge 0$, define $p_k(G)$ as the number of vertices with $p(v)\ge k$. We say that $p_k(G)$ is bounded for all $\HH$-free graphs if there exists a constant $c=c(\HH)$ such that $p_k(G)<c$ for all such graphs $G$. Here, a graph $G$ is said to be $\HH$-free if it contains no member of $\HH$ as an induced subgraph. When $p$ represents the degree of a vertex, Ramsey's theorem implies that $p_0(G)$ is bounded for every $\{K_n, E_n\}$-free graphs, where $K_n$ and $E_n$ denote the complete graph and the edgeless graph on $n$ vertices, respectively. The connected version of Ramsey's theorem says that $p_0(G)$ is bounded for all $\{K_n, P_n, K_{1,n}\}$-free connected graphs, where $P_n$ and $K_{1,n}$ are the $n$-vertex path and the star with $n$ leaves. In this paper, we extend the Ramsey's theorem to $p_2(G)$ where $p$ denotes the degree, the local independent number, the local component number, and sharp degree, that is, we characterize the forbidden family of graphs $\HH$ such that $p_2(G)$ is bounded for all (connected) $\HH$-free graphs. Moreover, we also characterize the forbidden family of graphs $\HH$ for which there is a constant $c=c(\HH)$ such that $p_c(G)$ is bounded for all $\HH$-free graphs. |
| title | Unavoidable induced subgraphs forced by graphs with many vertices of prescribed properties |
| topic | Combinatorics 05C07, 05C55, 05C75 |
| url | https://arxiv.org/abs/2512.04414 |