A note on partitions of groups

Abstract

Every infinite group $G$ of regular cardinality can be partitioned $G=A_1\cup A_2$ so that $G\neq FA_1$, $G\neq FA_2$ for every subset $F\subset G$ of cardinality $|F|<|G|$. The first author asked whether the same is true for each group $G$ of singular cardinality. We show that an answer depends on the algebraic structure of $G$. In particular, this is so for each free group but the statement does not hold for every Abelian group $G$ of singular cardinality. As an application, we prove that every Abelian group of singular cardinality k admits maximal translation invariant k-bounded topology that impossible for all groups of regular cardinality.