On minimal non-potentially closed subsets of the plane

Dominique Lecomte (1)

1 IMJ - Institut de Mathématiques de Jussieu

We study the Borel subsets of the plane that can be made closed by refining the Polish topology on the real line. These sets are called potentially closed. We first compare Borel subsets of the plane using products of continuous functions. We show the existence of a perfect antichain made of minimal sets among non-potentially closed sets. We apply this result to graphs, quasi-orders and partial orders. We also give a non-potentially closed set minimum for another notion of comparison. Finally, we show that we cannot have injectivity in the Kechris-Solecki-Todorcevic dichotomy about analytic graphs.

Mots clés: potentially; Baire classes; reduction; Hurewicz's Theorem

Domaines: Logique [math.LO]; Topologie générale [math.GN]

Dominique Lecomte. On minimal non-potentially closed subsets of the plane. Topology and its Applications, 2007, 154 (1), pp.241-262. ⟨hal-00175697⟩