Scott sentence complexities of linear orderings

Abstract

We study possible Scott sentence complexities of linear orderings using two approaches. First, we investigate the effect of the Friedman-Stanley embedding on Scott sentence complexity and show that it only preserves $\Pi^{\mathrm{in}}_{\alpha}$ complexities. We then take a more direct approach and exhibit linear orderings of all Scott complexities except $\Sigma^{\mathrm{in}}_{3}$ and $\Sigma^{\mathrm{in}}_{\lambda+1}$ for $\lambda$ a limit ordinal. We show that the former can not be the Scott sentence complexity of a linear ordering. In the process we develop new techniques which appear to be helpful to calculate the Scott sentence complexities of structures.