On asymorphisms of groups

Abstract

Let $G$, $H$ be groups and $κ$ be a cardinal. A bijection $f:G\to H$ is caled on asymorphism if, for any $X\in[G]^{<κ}$, $Y\in[H]^{<κ}$, there exist $X'\in[G]^{<κ}$, $Y'\in[H]^{<κ}$ such that for all $x\in G$ and $y\in H$, we have $f(Xx)\subseteq Y'f(x)$, $f^{-1}(Yy)\subseteq X'f^{-1}(y)$. For a set $S$, $[S]^{<κ}$ denotes the set $\{S'\subseteq S: |S'|<κ\}$. Let $κ$ and $γ$ be cardinals such that $\aleph_0<κ\leγ$. We prove that any two Abelian groups of cardinality $γ$ are $κ$-asymorphic, but the free group of rank $γ$ is not $κ$-asymorphic to an Abelian group provided that either $κ<γ$ or $κ=γ$ and $κ$ is a singular cardinal. It is known [7] that if $γ= κ$ and $κ$ is regular then any two groups of cardinality $κ$ are $κ$-asymorphic.