On the characterization of Souslin and Borel sets
Rolf–Dieter Reiss · Proceedings of the American Mathematical Society · 1975
Let X \mathfrak {X} be an arbitrary family of sets in the basic set X X . In this paper Souslin- X \mathfrak {X} sets are represented as projections on X X of certain σ δ \sigma \delta -sets in the cartesian product space of X X and the Baire space (or X X and the real line). For L - X L{\text { - }}\mathfrak {X} sets (i.e. Souslin sets defined with disjoint unions; ensembles d’unicité) injective projections are considered. The results also apply to Borel- X \mathfrak {X} sets since the system of L - X L{\text { - }}\mathfrak {X} sets includes the Borel- X \mathfrak {X} sets under suitable conditions.