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# Topology - Set-Theoretic

DMS Topology Seminar
Jan 18, 2023 01:00 PM
224 Parker Hall

Speaker: Arka Banerjee Title: Coarse cohomology of the complementAbstract: John Roe defined the notion of  Coarse cohomology of a metric space that measures the behavior at infinity of a space: more specifically, it measures the way in which uniformly large bounded sets fit together. In my talk I will give a brief introduction to this theory and define a new notion called "Coarse cohomology of the complement." Time permitting, I will discuss some related results and applications.

This talk is partly based on a joint work with Boris Okun.

DMS Topology Seminar
Nov 18, 2022 02:00 PM
224 Parker Hall and ZOOM

Speaker: Steven Clontz, University of South AlabamaTitle: Metrizability of Mahavier products indexed by partial orders

Abstract: Let $X$ be separable metrizable, and let $f\subseteq X^2$ be a non-trivial relation on $X$. For a given partial order $(P,\leq)$, the Mahavier product $M(X,f,P)\subseteq X^P$ (also known as a generalized inverse limit) collects functions such that $x(p)\in f(x(q))$ for all $p<q$. We will show that whenever $f$ satisfies condition $\Gamma$, $M(X,f,P)$ is separable metrizable if and only if $P$ is countable.

DMS Topology Seminar
Nov 11, 2022 02:00 PM
ZOOM

Speaker: Wlodek Kuperberg Title: Packing convex bodies in the plane and in space
DMS Topology Seminar
Nov 04, 2022 02:00 PM
224 Parker Hall and ZOOM

Speaker: Michel Smith

Title: Inverse limits on Hausdorff arcs that are hereditarily indecomposable are metric

Abstract: I will conclude my argument that a hereditarily indecomposable inverse limit of Hausdorff arcs is metric.  Note that a Hausdorff arc is a linearly ordered compact connected Hausdorff space and so is not necessarily metric.

DMS Set Theoretic Topology Seminar
Mar 06, 2020 02:00 PM
Parker Hall 246

Title: Character and tightness are discretely reflexive in compact spaces.

Abstract: We will show that tightness, character, sequentiality, and Frechet-Urysohn property are discretely reflexive in compact spaces, i.e., if $$X$$ is a compact space in which the closure of every discrete subset has a property $$P$$ from the list  $$tightness \leq \kappa, character\leq\kappa, sequentiality, Frechet-Urysohn property$$, then $$X$$ has the property $$P$$.

DMS Set Theoretic Topology Seminar
Feb 28, 2020 02:00 PM
Parker Hall 246

Title: Neither sigma-compactness nor Lindelof Sigma-property is discretely reflexive under CH

Abstract: We will construct, under the Continuum Hypothesis, an example of a space X in which the closure of every discrete set is countable (and hence sigma-compact) while X is not a Lindelof Sigma-space. Therefore, countability, sigma-compactness, and Lindelof Sigma-property all fail to be discretely reflexive under CH.

DMS Set Theoretic Topology Seminar
Feb 21, 2020 02:00 PM
Parker Hall 246

Title: Lindelof property is discretely reflexive in spaces of countable tightness.

Abstract: After finishing the construction of the example of a crowded countable space which is not weakly discretely generated,  we will start the proof of discrete reflexivity of the Lindelof property in spaces of countable tightness. In other words, we will prove that if $$X$$ is a space of countable tightness and the closure of every discrete subspace of $$X$$ is Lindelof, then $$X$$ itself is Lindelof. This non-trivial theorem of Arhangel'skii is not easy to prove even for first countable spaces.

DMS Set Theoretic Topology Seminar
Feb 14, 2020 02:00 PM
Parker Hall 246

Title: A countable space need not be weakly discretely generated

Abstract: We will construct a countable crowded Tychonoff space $$X$$ in which all discrete subsets are closed. This very non-trivial example of van Douwen shows that a discretely metrizable space is not necessarily first countable or even Frechet-Urysohn. This space has no non-trivial convergent sequences, every dense subspace of $$X$$ is open and every nowhere dense subset of $$X$$ is closed and discrete.

DMS Set Theoretic Topology Seminar
Feb 07, 2020 02:00 PM
Parker Hall 246

Title: Any monotonically normal space is discretely generated

Abstract: We will give the proof of the statement in the title and start to construct an example of countable crowded space in which every discrete subset is closed. This example shows, among other things, that not all countable spaces are discretely generated.

DMS Set Theoretic Topology Seminar
Jan 31, 2020 02:00 PM
Parker Hall 246