Randomness and the linear degrees of computability

We show that there exists a real α such that, for all reals β, if α is linear reducible to β (α ≤` β, previously denoted α ≤sw β) then β ≤T α. In fact, every random real satisfies this quasi-maximality property. As a corollary we may conclude that there exists no `-complete ∆2 real. Upon realizing that quasi-maximality does not characterize the random reals—there exist reals which are not random but which are of quasi-maximal `-degree—it is then natural to ask whether maximality could provide such a characterization. Such hopes, however, are in vain since no real is of maximal `-degree.