Structural properties of Q-degrees of n-c. e. sets

Abstract

In this paper we study structural properties of n-c. e. Q-degrees. Two theorems contain results on the distribution of incomparable Q-degrees. In another theorem we prove that every incomplete Π2 0 Q-degree forms a minimal pair in the c. e. degrees with a Δ2 0Q-degree. In a further theorem it is proved that there exists a c. e. Q-degree > 0 that is not half of a minimal pair in the c. e. Q-degrees. Crown Copyright © 2008.