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arXiv · 1611.06312

Actions of trees on semigroups, and an infinitary Gowers--Hales--Jewett Ramsey theorem

Martino Lupini
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Abstract

We introduce the notion of (Ramsey) action of a tree on a (filtered) semigroup. We then prove in this setting a general result providing a common generalization of the infinitary Gowers Ramsey theorem for multiple tetris operations, the infinitary Hales--Jewett theorems (for both located and nonlocated words), and the Farah--Hindman--McLeod Ramsey theorem for layered actions on partial semigroups. We also establish a polynomial version of our main result, recovering the polynomial Milliken--Taylor theorem of Bergelson--Hindman--Williams as a particular case. We present applications of our Ramsey-theoretic results to the structure of delta sets in amenable groups.

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Martino Lupini. 2016-11-19. Actions of trees on semigroups, and an infinitary Gowers--Hales--Jewett Ramsey theorem. https://arxiv.org/abs/1611.06312

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