English

On the maximum twist width of delta-matroids

Combinatorics 2026-02-03 v1

Abstract

For a ribbon graph GG, let γ(G)\gamma(G) denote its Euler genus. Recently, Chen, Gross and Tucker [J. Algebraic Combin. 63 (2026) 13] derived a formula for the maximum partial-dual Euler-genus γM(G)\partial\gamma_M(G) of a ribbon graph GG. Their key finding is that γM(G)\partial\gamma_M(G) can be achieved by a partial dual with respect to the edge set of a spanning quasi-tree. Moreover, they proposed the following problem: Given a ribbon graph GG, is there a sequence of edges e1,e2,,eke_1,e_2,\dots, e_k such that γ(G{e1,e2,,ek})=γM(G)\gamma(G^{\{e_1, e_2,\dots, e_k\}})=\partial\gamma_M(G) and such that the sequence γ(G),γ(G{e1}),,γ(G{e1,e2,,ek})\gamma(G), \gamma(G^{\{e_1\}}), \dots, \gamma(G^ {\{e_1, e_2,\dots, e_k\}}) rises monotonically (i.e., never decreasing) to γM(G)\partial\gamma_M(G)? Delta-matroids are set systems that satisfy the symmetric exchange axiom and serve as a matroidal abstraction of ribbon graphs. In this paper, we first show that the maximum twist width of a set system can be attained by twisting one of its feasible sets, which extends the result of Chen, Gross and Tucker to set systems. Then we solve the delta-matroid version of their problem, thereby providing an affirmative answer to the original problem for ribbon graphs.

Keywords

Cite

@article{arxiv.2602.01946,
  title  = {On the maximum twist width of delta-matroids},
  author = {Xian'an Jin and Zhuo Li and Qi Yan and Gang Zhang},
  journal= {arXiv preprint arXiv:2602.01946},
  year   = {2026}
}
R2 v1 2026-07-01T09:31:33.724Z