Effective powers of $\omega$ over ${\Delta }_2$ cohesive sets and infinite ${\Pi }_1$ sets without ${\Delta }_2$ cohesive subsets

Paul Shafer

A cohesive power of a computable structure is an effective ultrapower where a cohesive set acts as an ultrafilter. Let $\omega$, $\zeta$, and $\eta$ denote the respective order-types of the na…