arXiv subjects

Dániel Dobák

Publications and source records attributed to Dániel Dobák.

3 recordsLinked to original sources

arXiv2026

Recursive upper bounds for the vertex online Ramsey game with applications to hypergraph Ramsey numbers

The classical recursive upper bound on hypergraph Ramsey numbers due to Erdős and Rado states that for $2 \leq k < s \leq t$, \[ r_k(s,t) \leq 2^{\binom{r_{k-1}(s-1,t-1)}{k-1}}. \] In 2010, Conlon, Fox, and Sudakov introduced the so-called vertex online Ramsey numbers $\tilde{r}(s,t)$ for graphs to obtain a quantitative improvement over this bound when $k=3$. In this note, we show that the natural hypergraph generalization $\tilde{r}_k(s,t)$ of the vertex online Ramsey numbers satisfy an improved recurrence \[ \tilde{r}_k(s,t) \leq 2^{(1+o(1))\tilde{r}_{k-1}(s-1,t-1)}. \] We obtain several corollaries from this, including a lower-order improvement to the best known quantitative upper bounds for hypergraph Ramsey numbers and an improvement to the above recursive bound of Erdős and Rado.

math.CO↗

arXiv2024

Sharp exponents for bipartite Erdős-Rado numbers

The Erdős-Rado canonization theorem generalizes Ramsey's theorem to edge-colorings with an unbounded number of colors, in the sense that for $n = ER(m)$ sufficiently large, any edge-coloring of $E(K_n) \to \mathbb{N}$ will yield some copy of $K_m$ which is colored according to one of four canonical patterns. In this paper, we show that in the bipartite setting, the bipartite Erdős-Rado number $ER_B(m)$ satisfies \[ \log ER_B(m) = Θ(m \log m). \] Comparing this to the non-bipartite setting, the best known lower and upper bounds on $\log ER(m)$ are still separated by a factor of $\log m$.

math.CO↗

arXiv2022

Towards characterizing the 2-Ramsey equations of the form $ax+by=p(z)$

In this paper, we study a Ramsey-type problem for equations of the form $ax+by=p(z)$. We show that if certain technical assumptions hold, then any 2-colouring of the positive integers admits infinitely many monochromatic solutions to the equation $ax+by=p(z)$. This entails the $2$-Ramseyness of several notable cases such as the equation $ax+y=z^n$ for arbitrary $a\in\mathbb{Z}^{+}$ and $n\ge 2$, and also of $ax+by=a_Dz^D+\dots+a_1z\in\mathbb{Z}[z]$ such that $\text{gcd}(a,b)=1$, $D\ge 2$, $a,b,a_D>0$ and $a_1\neq0$.

math.CO↗