On the r. e. predecessors of d. r. e. degrees (Q1306796)

The author investigates the relationship between the recursively enumerable (r.e.) degrees, \(n\)-r.e. degrees and \(n\)-REA degrees for \(n\in\omega\). The following main results are obtained. (i) There are a d.r.e. degree \(d\) and an r.e. degree \(b\) below \(d\) such that \(b\) is just the minimum r.e. degree in which \(d\) is r.e. (ii) There exists an exact d.r.e. degree \(d>0\). (iii) There exists an isolated non-exact d.r.e. degree \(d>0\).