Hyperarithmetical index sets in recursion theory
Steffen Lempp · Transactions of the American Mathematical Society · 1987
We define a family of properties on hyperhypersimple sets and show that they yield index sets at each level of the hyperarithmetical hierarchy. An extension yields a Π 1 1 \Pi _1^1 -complete index set. We also classify the index set of quasimaximal sets, of coinfinite r.e. sets not having an atomless superset, and of r.e. sets major in a fixed nonrecursive r.e. set.