Probability measures on compact semitopological semigroups
This paper investigates the productivity of the Zariski topology of a group . If is a family of groups, and is their direct product, we prove that . This inclusion can be proper in general, and we describe the doubletons of abelian groups, for which the converse inclusion holds as well, i.e., . If is the identity element of a group , we also describe the class of groups such that is an elementary algebraic subset of for every group . We show among others, that is stable...
We discuss functions f : X × Y → Z such that sets of the form f (A × B) have non-empty interiors provided that A and B are non-empty sets of second category and have the Baire property.
Recall that a P-set is a closed set X such that the intersection of countably many neighborhoods of X is again a neighborhood of X. We show that if 𝔱 = 𝔠 then there is a minimal right ideal of (βℕ,+) that is also a P-set. We also show that the existence of such P-sets implies the existence of P-points; in particular, it is consistent with ZFC that no minimal right ideal is a P-set. As an application of these results, we prove that it is both consistent with and independent of ZFC that the shift...