The enumeration spectrum hierarchy of α-families and lowα degrees-lowα degrees for every computable
limit ordinal α is a degree spectrum of some algebraic structure.
Jump inversions of algebraic structures and Σ-definability show that this result does not hold for the
limit ordinal α = ω. Moreover, we prove
The enumeration spectrum hierarchy of α-families and lowα degrees-lowα degrees for every computable
limit ordinal α is a degree spectrum of some algebraic structure.
'Public sociology' past and present: specifying co-ordinates'Public sociology' past and present: specifying co-
ordinates Turing jumps in the Ershov hierarchy, where a stands for an
ordinal ωn > 1. © 2011 Springer Science+Business Media, Inc.