is no issue with induction. –  Carl Mummert Mar 16 at 13:49 feedback up vote 2 down vote Similar to @Alex's answer, there are also low sets. A set $A\subseteq \omega$ is low if $A' \leq 0'$ (so that $A' \equiv_{T} 0'$). Notice that any low $0<A<0'$ would then be a