We investigate effective categoricity of computable equivalence structures A. We show that A is computably categorical if and only if A has only finitely many finite equivalence classes, or A hasâ€¦ (More)

We investigate effective categoricity of computable Abelian p-groups A. We prove that all computably categorical Abelian p-groups are relatively computably categorical, that is, have computablyâ€¦ (More)

We consider only computable languages, and countable structures, with universe a subset of Ï‰, which we think of as a set of constants. We identify sentences with their GÃ¶del numbers. Thus, for aâ€¦ (More)

We study the relationship between algebraic structures and their inverse semigroups of partial automorphisms. We consider a variety of classes of natural structures including equivalence structures,â€¦ (More)

We construct a computable vector space with the trivial computable automorphism group, but with the dependence relations as complicated as possible, measured by their Turing degrees. As a corollary,â€¦ (More)

We compare Aut(Q), the classical automorphism group of a countable dense linear order, with Autc(Q), the group of all computable automorphisms of such an order. They have a number of similarities,â€¦ (More)