Tracing and domination in the Turing degrees


G. Barmpalias

Summary


We show that if 0' is c.e. traceable by a degree, then that degree is array non-computable. It follows that there is no minimal almost everywhere dominating degree, in the sense of Dobrinen and Simpson. This answers a question of Simpson and a question of Nies. Also it gives a natural definable property, namely non-minimality, which separates almost everywhere domination from highness.