A NOTE ON JUDICIOUS BISECTIONS OF GRAPHS

Abstract

Let G be a graph with m edges, minimum degree $\delta $ and containing no cycle of length 4. Answering a question of Bollobás and Scott, Fan et al. [‘Bisections of graphs without short cycles’, Combinatorics, Probability and Computing27(1) (2018), 44–59] showed that if (i) G is $2$ -connected, or (ii) $\delta \ge 3$ , or (iii) $\delta \ge 2$ and the girth of G is at least 5, then G admits a bisection such that $\max \{e(V_1),e(V_2)\}\le (1/4+o(1))m$ , where $e(V_i)$ denotes the number of edges of G with both ends in $V_i$ . Let $s\ge 2$ be an integer. In this note, we prove that if $\delta \ge 2s-1$ and G contains no $K_{2,s}$ as a subgraph, then G admits a bisection such that $\max \{e(V_1),e(V_2)\}\le (1/4+o(1))m$ .