A lower bound on the number of edges in DP-critical graphs
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arXiv
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| Auteurs principaux: | , , , |
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| Format: | Preprint |
| Publié: |
2024
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| _version_ | 1866910063731408896 |
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| author | Bradshaw, Peter Choi, Ilkyoo Kostochka, Alexandr Xu, Jingwei |
| author_facet | Bradshaw, Peter Choi, Ilkyoo Kostochka, Alexandr Xu, Jingwei |
| contents | A graph $G$ is $k$-critical (list $k$-critical, DP $k$-critical) if $χ(G)= k$ ($χ_\ell(G)= k$, $χ_\mathrm{DP}(G)= k$) and for every proper subgraph $G'$ of $G$, $χ(G')<k$ ($χ_\ell(G')< k$, $χ_\mathrm{DP}(G')<k$). Let $f(n, k)$ ($f_\ell(n, k), f_\mathrm{DP}(n,k)$) denote the minimum number of edges in an $n$-vertex $k$-critical (list $k$-critical, DP $k$-critical) graph. Our main result is that if $k\geq 5$ and $n\geq k+2$, then $$f_\mathrm{DP}(n,k)>\left(k - 1 + \left \lceil \frac{k^2 - 7}{2k-7} \right \rceil^{-1}\right)\frac{n}{2}.$$ This is the first bound on $f_\mathrm{DP}(n,k)$ that is asymptotically better than the well-known bound on $f(n,k)$ by Gallai from 1963. The result also yields a slightly better bound on $f_{\ell}(n,k)$ than the ones known before. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2409_00937 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | A lower bound on the number of edges in DP-critical graphs Bradshaw, Peter Choi, Ilkyoo Kostochka, Alexandr Xu, Jingwei Combinatorics 05C15, 05C35 A graph $G$ is $k$-critical (list $k$-critical, DP $k$-critical) if $χ(G)= k$ ($χ_\ell(G)= k$, $χ_\mathrm{DP}(G)= k$) and for every proper subgraph $G'$ of $G$, $χ(G')<k$ ($χ_\ell(G')< k$, $χ_\mathrm{DP}(G')<k$). Let $f(n, k)$ ($f_\ell(n, k), f_\mathrm{DP}(n,k)$) denote the minimum number of edges in an $n$-vertex $k$-critical (list $k$-critical, DP $k$-critical) graph. Our main result is that if $k\geq 5$ and $n\geq k+2$, then $$f_\mathrm{DP}(n,k)>\left(k - 1 + \left \lceil \frac{k^2 - 7}{2k-7} \right \rceil^{-1}\right)\frac{n}{2}.$$ This is the first bound on $f_\mathrm{DP}(n,k)$ that is asymptotically better than the well-known bound on $f(n,k)$ by Gallai from 1963. The result also yields a slightly better bound on $f_{\ell}(n,k)$ than the ones known before. |
| title | A lower bound on the number of edges in DP-critical graphs |
| topic | Combinatorics 05C15, 05C35 |
| url | https://arxiv.org/abs/2409.00937 |