A Feiner Look at the Intermediate Degrees

Denis R. Hirschfeldt, Asher M. Kach, Antonio Montalbán

We say that a set $S$ is ${\Delta }_{(n)}^0(X)$ if membership of $n$ in $S$ is a ${\Delta }_n^0(X)$ question, uniformly in $n$. A set $X$ is low for $\Delta$-Feiner if every set $S$ that is $Δ^0_{(n)…