Δ2 0 -copies of linear orderings

Abstract

It is proved that, for any n ω, there exist countable linear orderings Ln whose Δ 2 0 -spectrum consists of exactly all non n-low Δ 2 0 -degrees. Properties of such orderings are examined, for n = 1 and n = 2. © 2006 Springer Science+Business Media, Inc.