Minimal PI-systems with all points are multiply minimal
Zijie Lin, Kangbo Ouyang
TL;DR
The paper constructs a minimal subshift $(X^*,\sigma)$ that is an open proximal extension of its maximal equicontinuous factor (an odometer) and proves that every $x\in X^*$ is multiply recurrent minimal, i.e., $x^{(d)}$ is recurrent for $\tau_d$ for all $d\ge2$. The approach realizes multiple recurrence within finite words by an inductive word-construction guided by a key combinatorial Lemma $l:\mathrm{combin}$, inspired by Oprocha's doubly minimal example. This yields a minimal PI-system with all points multiply minimal, answering HSY22 in the affirmative. The paper also clarifies the structure around PI-systems via the structure theorem and demonstrates openness of the maximal equicontinuous-factor map to the odometer. Overall, the construction provides a new canonical example of a minimal PI-system with strong recurrence properties and a proximal-open extension to an equicontinuous factor.
Abstract
We construct a minimal subshift \((X^{*},σ)\) that serves as an open proximal extension of its maximal equicontinuous factor. We establish that every point in this subshift is multiply recurrent minimal. This work solves an open problem raised by Huang, Shao and Ye regarding the existence of minimal PI-systems such that each point is multiply minimal.
