Orderings with αth Jump Degree 0 (α)
Rodney G. Downey, Julia F. Knight · Proceedings of the American Mathematical Society · 1992
This paper completes an investigation of «jumps» of orderings. The last few cases are given in the proof that for each recursive ordinal α≥1 and for each Turing degree d≥0 (α) , there is a linear ordering A such that d is least among the αth jumps of degrees of (open diagrams of) isomorphic copies of A, and for β<α, the set of βth jumps of degrees of copies of A has no least element