Randomness, lowness and degrees


G. Barmpalias, A. Lewis and M. Soskova

Summary


We say that A is LR reducible to B if every B-random number is A-random. Intuitively this means that if oracle A can identify some patterns on some real, oracle B can also Ūnd patterns on the same real. In other words, B is at least as good as A for this purpose. We study the structure of the LR degrees globally and locally (i.e., restricted to the computably enumerable degrees) and their relationship with the Turing degrees. Among other results we show that whenever an oracle is not GL2 the LR degree of it bounds an uncountable set of degrees (so that, in particular, there exist LR degrees with uncountably many predecessors) and we give sample results which demonstrate how various techniques from the theory of the c.e. degrees can be used to prove results about the c.e. LR degrees.