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Tag Archives: powerdomain
Compact semilattices without small semilattices I: interval homomorphisms, products, and the Hoare hyperspace
I have already talked about compact semilattices before, but there is a lot more to say, especially on the subject of having small semilattices or not. Zhenchao Lyu is joining me this month, and we will pursue this next month. … Continue reading
Posted in Uncategorized
Tagged compactness, continuous dcpo, Hoare hyperspace, powerdomain, semilattice, Urysohn
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Strongly compact sets and the double hyperspace construction
The notion of strongly compact set is due to Reinhold Heckmann. A few months ago, I said that I would explain why the sobrification of the space Qfin(X) of finitary compact sets on a sober space X is not the … Continue reading
Posted in Uncategorized
Tagged compactness, hyperspace, powerdomain
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Topological lattices with small semilattices
I would like to explain a clever counterexample due to Jimmie Lawson in 1970, or rather a slight variant of it, pertaining to the theory of topological semilattices and to a property that crops up naturally, namely having small semilattices. … Continue reading
Posted in Uncategorized
Tagged algebra, hyperspace, lattice, monad, powerdomain, semilattice
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When do the upper (a.k.a., lower Vietoris) and Scott topologies coincide on the Hoare hyperspace of a space?
I would like to talk about a nifty, recent result due to Yu Chen, Hui Kou, and Zhenchao Lyu. There are two natural topologies on the Hoare hyperspace of a space X, the Scott and the lower Vietoris topology, and … Continue reading
Posted in Uncategorized
Tagged core-compactness, first-countability, hyperspace, powerdomain, Scott topology, Vietoris topology
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Irredundant families, the Smyth powerdomain, the Lyu-Jia theorem, and the baby Groemer theorem
A ∩-semilattice of sets is a family of sets that is closed under finite intersections, and it is irredundant if and only if all its non-empty elements are irreducible. That sounds like a ridiculously overconstrained notion, but I will give … Continue reading
Posted in Uncategorized
Tagged compactness, core-compactness, hyperspace, powerdomain
Comments Off on Irredundant families, the Smyth powerdomain, the Lyu-Jia theorem, and the baby Groemer theorem
First-countable spaces and their Smyth powerdomain
This month, we will look at certain conditions recently found by He, Li, Xi and Zhao in 2019, and then by Xu and Yang in 2021, in order to ensure that the Smyth powerdomain Q(X) (with the Scott topology) of … Continue reading
Posted in Uncategorized
Tagged first-countability, powerdomain
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The Sorgenfrey line is not consonant
In Exercise 5.4.12 of the book, I ask the reader to prove that neither the space of rationals, Q, nor the Sorgenfrey line, Rℓ, is consonant. But the proofs I had in mind were much too simple-minded to stand any … Continue reading
Posted in Uncategorized
Tagged consonance, counterexample, powerdomain, valuation
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Plotkin’s powerdomain and the hedgehog
There are three classical powerdomains in domain theory, named after Hoare, Smyth, and Plotkin. The first two are natural and well studied, and the third one is intricate and intriguing. To start with, there are several possible definitions for a … Continue reading
Posted in Uncategorized
Tagged counterexample, powerdomain
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Quasi-continuous domains and the Smyth powerdomain
“Quasi-continuous domains and the Smyth powerdomain” is the title of a very nice 2013 paper by Reinhold Heckmann and Klaus Keimel. I will not talk about quasi-continuous domains in this post. Rather, I will mention three pearls that this paper … Continue reading
Posted in Uncategorized
Tagged powerdomain, quasi-continuous domain
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