Yaojun Chen

activity

20232026

collaborators

22 papers

math.RT2026

Derived Picard reconstruction for graded surfaces with stops

Wen Chang, Dongjian Wu

We study reconstruction of graded surfaces with stops $(S, M, η)$ from their mapping class groups and the derived Picard groups of their partially wrapped Fukaya categories. In genus…

math.CO2026

Degree-square Turán problem for two self-converse tournaments

Zhuoran Han, Yaojun Chen

For a fixed digraph $F$ , let $ex_{2}^{+} (n, F)$ be the maximum of $\sum_{v \in V (D)} d_{D}^{+} (v)^{2}$ over all $n$ -vertex $F$ -free digraphs. Ai et al. [arXiv:2606.03520, 2026] a…

math.CO2026

Ramsey multiplicity and extremal colorings for odd cycles

Ting Huang, Junying Lu, Jiabao Yang +1

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

Counterexamples to two conjectures on the diameter of clique-free graphs

Hangdi Chen, Yaojun Chen

Erdős et al. (JCT-B, 1989) conjectured that, for integers $r \geq 2$ and $δ \geq 2$ with $3 r - 1 ∣ δ$ , every connected $K_{2 r + 1}$ -free graph of order $n$ and minimum degree $δ$ has diam…

math.CO2026

New upper bound for the Ramsey number of odd cycles

Ting Huang, Jiabao Yang, Yaojun Chen

The \emph{ $k$ -color Ramsey number} $R_{k} (C_{2 ℓ + 1})$ is the least integer $n$ such that any $k$ -edge-coloring of a complete graph $K_{n}$ has a monochromatic odd cycle $C_{2 ℓ + 1}$ …

math.CO2026

Erdős--Ko--Rado theorems in $ℓ_{2}$ -norm for three finite spaces

Qian Bao, Yaojun Chen, Yanbo Zhang

Let $F$ be a $k$ -uniform hypergraph. The famous Erdős--Ko--Rado (1961) theorem determines the maximum size and extremal structure for $F$ being $t$ -intersecting…

math.CO2026

On monochromatic path covers conjecture of Erdős--Gyárfás

Hangdi Chen, Yaojun Chen

Erdős and Gyárfás conjectured in 1995 that, in every red--blue edge-coloring of a complete graph $K_{n}$ , the vertex set can be covered by at most $n$ monochromatic paths, all…

math.CO2026

A note on tree-cycle Ramsey numbers

Ting Huang, Yanbo Zhang, Yaojun Chen

Let $R (T_{n}, C_{m})$ denote the Ramsey number of a tree $T_{n}$ on $n$ vertices versus a cycle $C_{m}$ of length $m$ . Burr, Erdős, Faudree, Rousseau, and Schelp (1982) asked for the least…

math.CO2026

Two-block cycles and chromatic number of Hamiltonian digraphs

Ruilin Zheng, Junying Lu, Xiaolin Wang +1

Let $k$ and $ℓ$ be positive integers. The family $C (k, ℓ)$ consists of all digraphs obtained from two internally vertex-disjoint directed paths of lengths at least $k$ and $\e…

math.CO2026

On regular homogeneously traceable nonhamiltonian graphs

Hangdi Chen, Yaojun Chen

A graph is homogeneously traceable if each vertex is an endpoint of a Hamiltonian path. Chartrand, Gould, and Kapoor (1979) proved irregular homogeneously traceable nonhamiltonian…

math.CO2026

Odd covers for complete graphs and complete 3-graphs

Ting Huang, Jiabao Yang, Yaojun Chen

The Graham-Pollak theorem says that one needs at least $n - 1$ complete bipartite graphs to cover each edge of a complete graph $K_{n}$ on $n$ vertices exactly once. The odd cover…

math.CO2026

The Turán number of the triangular pyramid of 4-layers

Hangdi Chen, Yaojun Chen, Xiutao Zhu

The Turán number $e x (n, H)$ of a graph $H$ is the maximum number of edges in any $H$ -free graph on $n$ vertices. The triangular pyramid of $k$ -layers, denoted by $T P_{k}$ , is a genera…

math.CO2025

Oriented trees in digraphs without short non-directed cycles

Junying Lu, Yaojun Chen

The girth of a graph $G$ is the length of a shortest cycle of $G$ . Jiang (JCT-B, 2001) showed that every graph $G$ with girth at least $2 ℓ + 1$ and minimum degree at least $k/\ell…

math.CO2025

Oriented diameter of graphs with given domination number

Xiaolin Wang, Yaojun Chen

Let $G$ be a connected bridgeless graph with domination number $γ$ . The oriented diameter (strong diameter) of $G$ is the smallest integer $d$ for which $G$ admits a strong orienta…

math.CO2025

Fan-goodness of sparse graphs

Ting Huang, Yanbo Zhang, Yaojun Chen

Let $G$ be a connected graph of order $n$ , $F_{k}$ be a fan consisting of $k$ triangles sharing a common vertex, and $t F_{k}$ be $t$ vertex-disjoint copies of $F_{k}$ . Brennan (2017) sho…

math.CO2025

Ramsey numbers of sparse graphs versus disjoint books

Ting Huang, Yanbo Zhang, Yaojun Chen

Let $B_{k}$ denote a book on $k + 2$ vertices and $t B_{k}$ be $t$ vertex-disjoint $B_{k}$ 's. For any integers $k \geq 2$ and $t \geq 1$ , there exists a positive constant $ε = ε (k, t)$ such that eve…

math.CO2025

Minimum degree and sparse connected spanning subgraphs

Ting Huang, Yanbo Zhang, Yaojun Chen

Let $G$ be a connected graph on $n$ vertices and at most $n (1 + ε)$ edges with bounded maximum degree, and $F$ a graph on $n$ vertices with minimum degree at least $n - k$ , where $ε$ i…

math.CO2025

Trichotomy and $t K_{m}$ -goodness of sparse graphs

Yanbo Zhang, Yaojun Chen

Let $G$ be a connected graph with $n$ vertices and $n + k - 2$ edges and $t K_{m}$ denote the disjoint union of $t$ complete graphs $K_{m}$ . In this paper, by developing a trichotomy for sp…

math.CO2024

Disproofs of four Gallai-Ramsey-type conjectures

Yanbo Zhang, Yaojun Chen

As a significant variation of Ramsey numbers, the Gallai-Ramsey number $G R_{k} (H)$ refers to the smallest positive integer $r$ such that, by coloring the edges of $K_{r}$ with at most…

math.CO2024

Generalized Turán problem for a path and a clique

Xiaona Fang, Xiutao Zhu, Yaojun Chen

Let $H$ be a family of graphs. The generalized Turán number $e x (n, K_{r}, H)$ is the maximum number of copies of the clique $K_{r}$ in any $n$ -vertex $H$ -…

math.CO2023

Ramsey goodness of fans

Yanbo Zhang, Yaojun Chen

Given two graphs $G_{1}$ and $G_{2}$ , the Ramsey number $r (G_{1}, G_{2})$ refers to the smallest positive integer $N$ such that any graph $G$ with $N$ vertices contains $G_{1}$ as a subgraph,…

math.CO2023

Maximum cliques in a graph without disjoint given subgraph

Fangfang Zhang, Yaojun Chen, Ervin Gyori +1

The generalized Turán number $\ex(n,K_s,F)$ denotes the maximum number of copies of $K_{s}$ in an $n$ -vertex $F$ -free graph. Let $k F$ denote $k$ disjoint copies of $F$ . Gerbner, Meth…

Derived Picard reconstruction for graded surfaces with stops

Degree-square Turán problem for two self-converse tournaments

Ramsey multiplicity and extremal colorings for odd cycles

Counterexamples to two conjectures on the diameter of clique-free graphs

New upper bound for the Ramsey number of odd cycles

Erdős--Ko--Rado theorems in ℓ2​-norm for three finite spaces

On monochromatic path covers conjecture of Erdős--Gyárfás

A note on tree-cycle Ramsey numbers

Two-block cycles and chromatic number of Hamiltonian digraphs

On regular homogeneously traceable nonhamiltonian graphs

Odd covers for complete graphs and complete 3-graphs

The Turán number of the triangular pyramid of 4-layers

Oriented trees in digraphs without short non-directed cycles

Oriented diameter of graphs with given domination number

Fan-goodness of sparse graphs

Ramsey numbers of sparse graphs versus disjoint books

Minimum degree and sparse connected spanning subgraphs

Trichotomy and tKm​-goodness of sparse graphs

Disproofs of four Gallai-Ramsey-type conjectures

Generalized Turán problem for a path and a clique

Ramsey goodness of fans

Maximum cliques in a graph without disjoint given subgraph

Erdős--Ko--Rado theorems in $ℓ_{2}$ -norm for three finite spaces

Trichotomy and $t K_{m}$ -goodness of sparse graphs