Isolated maximal d.r.e. degrees

Abstract

There are very few results about maximal d.r.e. degrees as the construction is very hard to work with other requirements. In this paper we show that there exists an isolated maximal d.r.e. degree. In fact, we introduce a closely related notion called (m,n)-cupping degree and show that there exists an isolated (2,ω)-cupping degree, and there exists a proper (2,1)-cupping degree. It helps understanding various degree structures in the Ershov Hierarchy.