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arXiv · 1512.09252

The Lelek fan and the Poulsen simplex as Fraïssé limits

Wiesław Kubiś·Aleksandra Kwiatkowska
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Abstract

We describe the Lelek fan, a smooth fan whose set of end-points is dense, and the Poulsen simplex, a Choquet simplex whose set of extreme points is dense, as Fraïssé limits in certain natural categories of embeddings and projections. As an application we give a short proof of their uniqueness, universality, and almost homogeneity. We further show that for every two countable dense subsets of end-points of the Lelek fan there exists an auto-homeomorphism of the fan mapping one set onto the other. This improves a result of Kawamura, Oversteegen, and Tymchatyn from 1996.

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Wiesław Kubiś, Aleksandra Kwiatkowska. 2016-12-18. The Lelek fan and the Poulsen simplex as Fraïssé limits. https://arxiv.org/abs/1512.09252

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