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Zoltán Szentmiklóssy

Publications and source records attributed to Zoltán Szentmiklóssy.

21 records · Page 2Linked to original sources

Between countably compact and $ω$-bounded

Given a property $P$ of subspaces of a $T_1$ space $X$, we say that $X$ is {\em $P$-bounded} iff every subspace of $X$ with property $P$ has compact closure in $X$. Here we study $P$-bounded spaces for the properties $P \in \{ωD, ωN, C_2 \}$ where $ωD \, \equiv$ "countable discrete", $ωN \, \equiv$ "countable nowhere dense", and $C_2 \,\equiv$ "second countable". Clearly, for each of these $P$-bounded is between countably compact and $ω$-bounded. We give examples in ZFC that separate all these boundedness properties and their appropriate combinations. Consistent separating examples with better properties (such as: smaller cardinality or weight, local compactness, first countability) are also produced. We have interesting results concerning $ωD$-bounded spaces which show that $ωD$-boundedness is much stronger than countable compactness: $\bullet$ Regular $ωD$-bounded spaces of Lindelöf degree $< cov(\mathcal{M})$ are $ω$-bounded. $\bullet$ Regular $ωD$-bounded spaces of countable tightness are $ωN$-bounded, and if $\mathfrak{b} > ω_1$ then even $ω$-bounded. $\bullet$ If a product of Hausdorff space is $ωD$-bounded then all but one of its factors must be $ω$-bounded. $\bullet$ Any product of at most $\mathfrak{t}$ many Hausdorff $ωD$-bounded spaces is countably compact. As a byproduct we obtain that regular, countably tight, and countably compact spaces are discretely generated.

math.GN↗

Conflict free colorings of (strongly) almost disjoint set-systems

A set-system $X$ is a $(λ, κ,μ)$-system iff $|X|=λ$, $|x|=κ$ for each $x\in X$, and $X$ is $μ$-almost disjoint. We write $[λ, κ, μ] -> ρ$ iff every $(λ, κ,μ)$-system has a "conflict free coloring with $ρ$ colors", i.e. there is a coloring of the elements of $\cup X$ with$ρ$ colors such that for each element $x$ of $X$ there is a color $ξ<ρ$ such that exactly one element of $x$ has color $ξ$. Our main object of study is the relation $[λ, κ, μ] -> ρ$. We give full description of this relation when $κ$ is finite. We also show that if $d$ is a natural number then $[λ,κ,d]-> ω$ always holds. Under GCH we prove that $[λ,κ,ω]-> ω_2$ holds for $κ>ω_1$, but the relation $[λ,κ,ω]-> ω_1$ is independent (modulo some large cardinals).

math.LO↗

Cardinal sequences and Cohen real extensions

We show that if we add any number of Cohen reals to the ground model then, in the generic extension, a locally compact scattered space has at most (2^{aleph_0})^V many levels of size omega. We also give a complete ZFC characterization of the cardinal sequences of regular scattered spaces. Although the classes of the regular and of the 0-dimensional scattered spaces are different, we prove that they have the same cardinal sequences.

math.LO↗