The continuity of cupping to \(\text \textbf{0}'\)
Let \({\mathbf a}\) and \({\mathbf b}\) be recursively enumerable (r.e.) Turing degrees less than \(\mathbf{0}'\) such that \({\mathbf a}\cup {\mathbf b}=\text{\textbf{0}}'\). A degree \({\mathbf c}\) is called a major subdegree of \({\mathbf a}\) if \({\mathbf c}< {\mathbf a}\) and \({\mathbf c}\cup {\mathbf b}= \mathbf{0}'\). It is unknown whether every r.e. degree \({\mathbf a}\) except \(\mathbf{0}\) and \(\mathbf{0}'\) has a major subdegree. In the paper, a group of well-known specialists gives a particular answer to this question.
scientific article; zbMATH DE number 503600