Quotient sets and density recurrent sets
Quotient sets and density recurrent sets
Let $S$ be a left amenable semigroup. Say that a subset $A$ of $S$ is large if there is some left invariant mean $\mu$ on $S$ with $\mu (\chi _A)>0$. A subset $B$ of $S$ is density recurrent if and only if, whenever $A$ is a large subset of $S$, …