Minimal pairs in initial segments of the recursively enumerable degrees

We show that for every r.e. Turing degreea>0, there is an r.e. degreeb<a which is not half of a minimal pair in the initial segment 0, a]. This work was partially supported by National Science Foundation Grant DMS88-00030 to Stob, the New Zealand Marsden Fund for Basic Research in Science Grant VIC-509 to Downey, and New Zealand-United States Cooperative Science Program Grant INT90-20558 from the National Science Foundation to both authors. The authors thank the referee for several helpful comments.