English

Irregular subgraph in a regular graph

Combinatorics 2026-07-07 v1

Abstract

A conjecture of Alon and Wei states that, for any dd-regular graph GG with nn vertices, there exists a spanning subgraph HH such that for all 0id0\le i\le d, we have m(H,i)m(H, i), the number of vertices in HH with degree ii, is between nd+12\frac{n}{d+1}-2 and nd+1+2\frac{n}{d+1}+2. We prove the conjecture for all fixed dd when nn is sufficiently large. More precisely, if q=(q0,,qd)q=(q_0,\ldots,q_d) satisfies i=0dqi=n,i=0diqi0(mod2),qind+11(0id), \sum_{i=0}^d q_i=n,\qquad \sum_{i=0}^d i q_i\equiv 0\pmod 2,\qquad \left|q_i-\frac{n}{d+1}\right|\le 1 \quad (0\le i\le d), then there is a spanning subgraph HGH\subseteq G such that m(H,i)=qi(0id). m(H,i)=q_i \qquad (0\le i\le d).

Cite

@article{arxiv.2607.06465,
  title  = {Irregular subgraph in a regular graph},
  author = {Tianyue Cao and Quanyu Tang and Hehui Wu},
  journal= {arXiv preprint arXiv:2607.06465},
  year   = {2026}
}

Comments

18 pages. Comments and suggestions are welcome