Computably Enumerable Reals and Uniformly Presentable Ideals

We study the relationship between a computably enumerable real and its presentations. A set A presents a computably enumerable real α if A is a computably enumerable prefix-free set of strings such that α = ∑ σ∈A 2 −|σ|. Note that ∑ σ∈A 2 −|σ| is precisely the measure of the set of reals that have a string in A as an initial segment. So we will simply abbreviate ∑ σ∈A 2 −|σ| by μ(A). It is known that whenever A so presents α then A ≤wtt α, where ≤wtt denotes weak truth table reducibility, and that the wtt degrees of presentations form an ideal I(α) in the computably enumerable wtt degrees. We prove that any such ideal is Σ3, and conversely that if I is any Σ3 ideal in the computably enumerable wtt degrees then there is a computable enumerable real α such that I = I(α).