10 research outputs found
First Order Theories of Some Lattices of Open Sets
We show that the first order theory of the lattice of open sets in some
natural topological spaces is -equivalent to second order arithmetic. We
also show that for many natural computable metric spaces and computable domains
the first order theory of the lattice of effectively open sets is undecidable.
Moreover, for several important spaces (e.g., , , and the
domain ) this theory is -equivalent to first order arithmetic
Ideal presentations and numberings of some classes of effective quasi-Polish spaces
The well known ideal presentations of countably based domains were recently
extended to (effective) quasi-Polish spaces. Continuing these investigations,
we explore some classes of effective quasi-Polish spaces. In particular, we
prove an effective version of the domain-characterization of quasi-Polish
spaces, describe effective extensions of quasi-Polish topologies, discover
natural numberings of classes of effective quasi-Polish spaces, estimate the
complexity of the (effective) homeomorphism relation and of some classes of
spaces w.r.t. these numberings, and investigate degree spectra of continuous
domains
Overt choice
We introduce and study the notion of overt choice for countably-based spaces and for CoPolish spaces. Overt choice is the task of producing a point in a closed set specified by what open sets intersect it. We show that the question of whether overt choice is continuous for a given space is related to topological completeness notions such as the Choquet-property; and to whether variants of Michael’s selection theorem hold for that space. For spaces where overt choice is discontinuous it is interesting to explore the resulting Weihrauch degrees, which in turn are related to whether or not the space is Fréchet–Urysohn
Computability on quasi-Polish spaces
International audienceWe investigate the effectivizations of several equivalent definitions of quasi-Polish spaces and study which characterizations hold effectively. Being a computable effectively open image of the Baire space is a robust notion that admits several characterizations. We show that some natural effectivizations of quasi-metric spaces are strictly stronger
Comparing computability in two topologies
Computable analysis provides ways of representing points in a topological space, and therefore of defining a notion of computable points of the space. In this article, we investigate when two topologies on the same space induce different sets of computable points. We first study a purely topological version of the problem, which is to understand when two topologies are not σ-homeomorphic. We obtain a characterization leading to an effective version, and we prove that two topologies satisfying this condition induce different sets of computable points. Along the way, we propose an effective version of the Baire category theorem which captures the construction technique, and enables one to build points satisfying properties that are co-meager w.r.t. a topology, and are computable w.r.t. another topology. Finally, we generalize the result to three topologies and give an application to prove that certain sets do not have computable type, i.e. have a homeomorphic copy that is semicomputable but not computable