On Computability Theoretic Properties of Structures and Their Cartesian Products
Bakhadyr Khoussainov Β· Mathematical logic quarterly Β· 2000
In this paper we show that for any set X β Ο there exists a structure π that has no presentation computable in X such that π2 has a computable presentation. We also show that there exists a structure π with infinitely many computable isomorphism types such that π2 has exactly one computable isomorphism type.