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math.LO2026
The epimorphism relation among countable groups is a complete analytic quasi-order
Su Gao, Feng Li, André Nies +1
We prove that the epimorphism relation is a complete analytic quasi-order on the space of countable groups. In the process, we obtain the result of independent interest that the ep…
math.LO2026
Procountable groups are not classifiable by countable structures
Su Gao, André Nies, Gianluca Paolini
We prove that topological isomorphism on procountable groups is not classifiable by countable structures, in the sense of descriptive set theory. In fact, the equivalence relation…
math.LO2025
Open Problems in Computability Theory and Descriptive Set Theory
George Barmpalias, Nikolay Bazhenov, Chi Tat Chong +11
These open problems were presented in the Problem Sessions held during the Tianyuan Workshop on Computability Theory and Descriptive Set Theory, June 16-20, 2025. The problems are…