Structural vs. computational complexity

Abstract

We consider highness in the context of computable structure theory and, particularly, the Scott rank of a structure. We define highness for Scott rank and highness for computably defined Scott rank $α$ and characterize them in terms of the ability to compute $Δ^0_β$ sets for appropriate $β$. We close with a discussion of the index sets of structures with a given Scott rank or computably defined Scott rank and a few words about highness for noncomputable Scott ranks.