# On problems about judicious bipartitions of graphs

## TL;DR

This paper investigates bipartitions of graphs, confirming a conjecture for some realizations, providing counterexamples to refine bounds, and studying edge distributions with new bounds and answers to open questions.

## Contribution

It proves the Bollobás-Scott conjecture for certain graph realizations, presents counterexamples suggesting a revised bound, and establishes optimal bounds on bipartition edge distributions.

## Key findings

- Confirmed the Bollobás-Scott conjecture for some graph realizations.
- Provided infinite counterexamples indicating the need for a revised bound.
- Established optimal bounds on bipartition edge sums and answered related open questions.

## Abstract

Bollob\'{a}s and Scott [5] conjectured that every graph $G$ has a balanced bipartite spanning subgraph $H$ such that for each $v\in V(G)$, $d_H(v)\ge (d_G(v)-1)/2$. In this paper, we show that every graphic sequence has a realization for which this Bollob\'{a}s-Scott conjecture holds, confirming a conjecture of Hartke and Seacrest [10]. On the other hand, we give an infinite family of counterexamples to this Bollob\'{a}s-Scott conjecture, which indicates that $\lfloor (d_G(v)-1)/2\rfloor$ (rather than $(d_G(v)-1)/2$) is probably the correct lower bound. We also study bipartitions $V_1, V_2$ of graphs with a fixed number of edges. We provide a (best possible) upper bound on $e(V_1)^{\lambda}+e(V_2)^{\lambda}$ for any real $\lambda\geq 1$ (the case $\lambda=2$ is a question of Scott [13]) and answer a question of Scott [13] on $\max\{e(V_1),e(V_2)\}$.