Friedberg numberings in the Ershov hierarchy

Serikzhan A. Badaev, Mustafa Manat, Andrea Sorbi
2014 Archive for Mathematical Logic  
We show that for every n ≥ 1, there exists a Σ −1 n -computable family which up to equivalence has exactly one Friedberg numbering which does not induce the least element of the corresponding Rogers semilattice.
doi:10.1007/s00153-014-0402-y fatcat:52zsc6vsevgmxcaeaguogpmzqq