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A graph $H$ is said to be common if the number of monochromatic labelled copies of $H$ in a red/blue edge colouring of a large complete graph is asymptotically minimized by a random colouring with an equal proportion of each colour. We…

组合数学 · 数学 2025-09-16 Natalie Behague , Natasha Morrison , Jonathan A. Noel

A graph $H$ is common if the number of monochromatic copies of $H$ in a 2-edge-colouring of the complete graph $K_n$ is asymptotically minimised by the random colouring. We prove that, given $k,r>0$, there exists a $k$-connected common…

组合数学 · 数学 2023-06-14 Sejin Ko , Joonkyung Lee

A graph H is common if the number of monochromatic copies of H in a 2-edge-coloring of the complete graph is asymptotically minimized by the random coloring. The classification of common graphs is one of the most intriguing problems in…

组合数学 · 数学 2022-04-28 Robert Hancock , Daniel Kral , Matjaz Krnc , Jan Volec

A graph $H$ is common if its Ramsey multiplicity, i.e., the minimum number of monochromatic copies of $H$ contained in any $2$-edge-coloring of $K_n$, is asymptotically the same as the number of monochromatic copies in the random…

组合数学 · 数学 2025-09-23 Daniel Kráľ , Matjaž Krnc , Ander Lamaison

A graph $H$ is called strongly common if for every coloring $\phi$ of $K_n$ with two colors, the number of monochromatic copies of $H$ is at least the number of monochromatic copies of $H$ in a random coloring of $K_n$ with the same density…

组合数学 · 数学 2023-05-19 Leo Versteegen

Ramsey's Theorem guarantees for every graph H that any 2-edge-coloring of a sufficiently large complete graph contains a monochromatic copy of H. In 1962, Erdos conjectured that the random 2-edge-coloring minimizes the number of…

组合数学 · 数学 2024-08-22 Daniel Kral , Jan Volec , Fan Wei

A graph H is k-common if the number of monochromatic copies of H in a k-edge-coloring of K_n is asymptotically minimized by a random coloring. For every k, we construct a connected non-bipartite k-common graph. This resolves a problem…

组合数学 · 数学 2024-08-27 Daniel Kral , Jonathan A. Noel , Sergey Norin , Jan Volec , Fan Wei

A graph H is called common if the total number of copies of H in every graph and its complement asymptotically minimizes for random graphs. A former conjecture of Burr and Rosta, extending a conjecture of Erdos asserted that every graph is…

组合数学 · 数学 2017-07-31 Hamed Hatami , Jan Hladky , Daniel Kral , Serguei Norine , Alexander Razborov

Goodman proved that the sum of the number of triangles in a graph on $n$ nodes and its complement is at least $n^3/24$; in other words, this sum is minimized, asymptotically, by a random graph with edge density $1/2$. Erd\H{o}s conjectured…

组合数学 · 数学 2019-12-09 Endre Csóka , Tamás Hubai , László Lovász

A graph $H$ is said to be common if the number of monochromatic labelled copies of $H$ in a $2$-colouring of the edges of a large complete graph is asymptotically minimized by a random colouring. It is well known that the disjoint union of…

组合数学 · 数学 2025-12-09 Jae-baek Lee , Jonathan A. Noel

A graph H is common if the number of monochromatic copies of H in a 2-edge-colouring of the complete graph is minimised by the random colouring. Burr and Rosta, extending a famous conjecture by Erdos, conjectured that every graph is common.…

组合数学 · 数学 2022-04-28 Andrzej Grzesik , Joonkyung Lee , Bernard Lidický , Jan Volec

A graph $H$ is common if the limit as $n\to\infty$ of the minimum density of monochromatic labelled copies of $H$ in an edge colouring of $K_n$ with red and blue is attained by a sequence of quasirandom colourings. We apply an…

组合数学 · 数学 2023-07-11 Natalie Behague , Natasha Morrison , Jonathan A. Noel

The Ramsey multiplicity constant of a graph $H$ is the minimum proportion of copies of $H$ in the complete graph which are monochromatic under an edge-coloring of $K_n$ as $n$ goes to infinity. Graphs for which this minimum is…

组合数学 · 数学 2018-03-29 Jessica De Silva , Xiang Si , Michael Tait , Yunus Tunçbilek , Ruifan Yang , Michael Young

A graph $H$ is \emph{common} if the number of monochromatic copies of $H$ in a 2-edge-colouring of the complete graph $K_n$ is asymptotically minimised by the random colouring, or equivalently, $t_H(W)+t_H(1-W)\geq 2^{1-e(H)}$ holds for…

组合数学 · 数学 2022-10-04 Jang Soo Kim , Joonkyung Lee

We study the rainbow version of the graph commonness property: a graph $H$ is $r$-rainbow common if the number of rainbow copies of $H$ (where all edges have distinct colors) in an $r$-coloring of edges of $K_n$ is maximized asymptotically…

组合数学 · 数学 2024-07-11 Yihang Sun

A graph is $H$-Ramsey if every two-coloring of its edges contains a monochromatic copy of $H$. Define the $F$-Ramsey number of $H$, denoted by $r_F(H)$, to be the minimum number of copies of $F$ in a graph which is $H$-Ramsey. This…

组合数学 · 数学 2025-10-13 Jacob Fox , Jonathan Tidor , Shengtong Zhang

The Unfriendly Partition Conjecture posits that every countable graph admits a 2-colouring in which for each vertex there are at least as many bichromatic edges containing that vertex as monochromatic ones. This is not known in general, but…

组合数学 · 数学 2023-03-22 John Haslegrave

For a fixed graph $H$, what is the smallest number of colours $C$ such that there is a proper edge-colouring of the complete graph $K_n$ with $C$ colours containing no two vertex-disjoint colour-isomorphic copies, or repeats, of $H$? We…

组合数学 · 数学 2021-06-28 David Conlon , Mykhaylo Tyomkyn

A strong odd coloring of a simple graph $G$ is a proper coloring of the vertices of $G$ such that for every vertex $v$ and every color $c$, either $c$ is used an odd number of times in the open neighborhood $N_G(v)$ or no neighbor of $v$ is…

组合数学 · 数学 2024-10-04 Yair Caro , Mirko Petruševski , Riste Škrekovski , Zsolt Tuza

Let $H$ be a graph with $\Delta(H) \leq 2$, and let $G$ be obtained from $H$ by gluing in vertex-disjoint copies of $K_4$. We prove that if $H$ contains at most one odd cycle of length exceeding $3$, or if $H$ contains at most $3$…

组合数学 · 数学 2021-07-08 Jessica McDonald , Gregory J. Puleo
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