Yaojun Chen

activity

20222026

collaborators

12 papers

math.CO2026

Any $k$ -graph with zero $ℓ$ -degree Turán density is layered

Jiabao Yang, Xiaona Fang, Yaojun Chen

The codegree Turán density $π_{co} (F)$ is the supremum over all $γ \in [0, 1)$ such that, for arbitrarily large $n$ , there exists an $n$ -vertex $F$ -free $k$ -graph $H$ whose…

math.CO2026

On the codegree Turán density of projective geometries

Xiaona Fang, Yaojun Chen

Let $F$ be a $k$ -uniform hypergraph, abbreviated as $k$ -graph. The codegree Turán density $γ (F)$ is the supremum over all $γ \in [0, 1)$ such that, for arbitrarily large $n$ , there e…

math.CO2026

On linear $k$ -graphs with codegree Turán density arbitrarily close to zero

Xiaona Fang, Yaojun Chen

Let $F$ be a $k$ -uniform hypergraph, abbreviated as $k$ -graph. The codegree Turán density $π_{co} (F)$ is the supremum over all $γ \in [0, 1)$ such that, for arbitrarily larg…

math.CO2026

On the threshold Ramsey multiplicity conjectures for paths and even cycles

Ting Huang, Jiabao Yang, Yaojun Chen

The Ramsey number $r (H)$ of a graph $H$ is the minimum positive integer $n$ such that every red/blue edge-coloring of the complete graph $K_{n}$ on $n$ vertices contains a monochroma…

math.CO2026

Ramsey numbers and Gallai--Ramsey numbers of disjoint unions of cherries

Yanbo Zhang, Qian Chen, Yaojun Chen

For graphs $G_{1}, \dots, G_{k}$ , the Ramsey number $R (G_{1}, \dots, G_{k})$ is the smallest positive integer $N$ such that every $k$ -edge-coloring of $K_{N}$ contains a monochromatic copy of…

math.CO2026

New bounds for Ramsey numbers involving graphs with a center

Yanbo Zhang, Yaojun Chen

Let $F_{n}$ , $W_{n}$ , and $K_{n}$ be the graphs obtained by joining a vertex to $n$ independent edges, a cycle and a path of order $n - 1$ , respectively. In this paper, we give n…

math.CO2024

Oriented Ramsey numbers of some sparse graphs

Junying Lu, Yaojun Chen

Let $H$ be an oriented graph without directed cycle. The oriented Ramsey number of $H$ , denoted by $r (H)$ , is the smallest integer $N$ such that every tournament o…

math.CO2023

Extremal problems for a matching and any other graph

Xiutao Zhu, Yaojun Chen

For a family of graphs $\F$, a graph is called $\F$-free if it does not contain any member of $\F$ as a subgraph. The generalized Turán number $\ex(n,K_r,\F)$ is the maximum number…

math.CO2023

The Turán number of path-star forests

Xiaona Fang, Yaojun Chen, Lihua You

The Turán number of a graph $H$ , denoted by $e x (n, H)$ , is the maximum number of edges in any graph on $n$ vertices containing no $H$ as a subgraph. A linear (star) forest is a fore…

math.CO2023

The hat guessing number of random graphs with constant edge-chosen probability

Lanchao Wang, Yaojun Chen

Let $G$ be a graph with $n$ vertices. The {\em hat guessing number} of $G$ is defined in terms of the following game: There are $n$ players and one opponent. The opponent will wear…

math.CO2023

Connectedness of friends-and-strangers graphs of complete bipartite graphs and others

Lanchao Wang, Junying Lu, Yaojun Chen

Let $X$ and $Y$ be any two graphs of order $n$ . The friends-and-strangers graph $FS (X, Y)$ of $X$ and $Y$ is a graph with vertex set consisting of all bijections $σ:V(X) \m…

math.CO2022

The connectedness of the friends-and-strangers graph of lollipop graphs and others

Lanchao Wang, Yaojun Chen

Let $X$ and $Y$ be any two graphs of order $n$ . The friends-and-strangers graph $FS (X, Y)$ of $X$ and $Y$ is a graph with vertex set consisting of all bijections $σ:V(X) \m…

Any k-graph with zero ℓ-degree Turán density is layered

On the codegree Turán density of projective geometries

On linear k-graphs with codegree Turán density arbitrarily close to zero

On the threshold Ramsey multiplicity conjectures for paths and even cycles

Ramsey numbers and Gallai--Ramsey numbers of disjoint unions of cherries

New bounds for Ramsey numbers involving graphs with a center

Oriented Ramsey numbers of some sparse graphs

Extremal problems for a matching and any other graph

The Turán number of path-star forests

The hat guessing number of random graphs with constant edge-chosen probability

Connectedness of friends-and-strangers graphs of complete bipartite graphs and others

The connectedness of the friends-and-strangers graph of lollipop graphs and others

Any $k$ -graph with zero $ℓ$ -degree Turán density is layered

On linear $k$ -graphs with codegree Turán density arbitrarily close to zero