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Author Archives: jgl
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
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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
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Tagged powerdomain, quasi-continuous domain
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Quasi-uniform spaces IV: Formal balls—a proposal
Formal balls are an extraordinarily useful notion in the study of quasi-metric, and even hemi-metric spaces. Is there any way of extending the notion to the case of quasi-uniform spaces? This is what I would like to start investigating. This … Continue reading
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Tagged formal ball, quasi-uniform space
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Quasi-uniform spaces III: Smyth-completeness, symcompactness
We embark on the study of notions of completeness for quasi-uniform spaces, and we concentrate on Smyth-completeness. We will see that at least two familiar theorems from the realm of quasi-metric spaces generalize to quasi-uniform spaces: all Smyth-complete quasi-uniform spaces … Continue reading
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Tagged completeness, quasi-uniform space
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Quasi-uniform spaces II: Stably compact spaces
There is a standard result in the theory of uniform spaces that shows (again) how magical compact Hausdorff space can be: for every compact Hausdorff space X, there is a unique uniformity that induces the topology of X, and its … Continue reading
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Tagged quasi-uniform space, stably compact space
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Quasi-Uniform Spaces I: Pervin Quasi-Uniformities, Pervin Spaces
A uniform space is a natural generalization of the notion of a metric space, on which completeness still makes sense. It is rather puzzling that I managed to avoid the subject of quasi-uniform spaces in something like the 7 years … Continue reading
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Tagged quasi-uniform space
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On the word topology, and beyond
Today I (Jean G.-L.) have the pleasure to have a guest, Aliaume Lopez. We are going to talk about the word topology on X*. In the book, there is a so-called Topological Higman Lemma that says that, if X is … Continue reading
Chains and nested spaces
A chain is a totally ordered poset, and a nested space is a topological space whose lattice of open sets is a chain. That may seem like a curious notion, although you might say that the Scott topology on the … Continue reading
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Tagged chain, continuous lattice, minimal topology, TD space, valuation
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TD spaces
In any topological space, the closure of any one-element set {x} is also its downward closure ↓x with respect to the specialization preordering. A TD space is a topological space in which, for every point x, ↓x – {x} is … Continue reading
Zhao, Xi and Chen’s well-filtered, non-sober dcpo
There are several known examples of dcpos that are well-filtered, but not sober, and I have already mentioned one due to Xiaodong Jia. I would like to explain another one, due to Dongsheng Zhao, Xiaoyong Xi, and Yixiang Chen. This … Continue reading
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Tagged counterexample, sober space, well-filtered space
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