Generalized heredity in $\mathcal B$-free systems

Abstract

Let $\mathcal B\subseteq\mathbb N$ be a primitive set. We complement results on heredity of the $\mathcal B$-free subshift $X_\eta$ from [arxiv:1509.08010] in two directions: In the proximal case we prove that a subshift $X_\varphi$, which micht be slightly larger than the subshift $X_\eta$, is always hereditary. (There is no need to assume that the set $\mathcal B$ is taut or even has light tails, but if $\mathcal B$ is taut, then $X_\varphi=X_\eta$.) We also generalize the the concept of heredity to the non-proximal (and hence non-hereditary) case by proving that $X_\varphi$ is always "hereditary away from its unique minimal subsystem" (which is always Toeplitz). Finally we characterize regularity of this Toeplitz subsystem equivalently by the condition $m_H(\overline{\operatorname{int}(W)})=0$, where $W$ ("the window") is a subset of a compact abelian group $H$ canonically associated with the set $\mathcal B$, and $m_H$ denotes Haar measure on $H$. Throughout, results from [arxiv:1702.02375] are heavily used.