Turing degree;
n-recursively enumerable;
undecidability;
Sigma(1)-substructure;
DRE DEGREES;
D O I:
10.1142/S0219061312500055
中图分类号:
O1 [数学];
学科分类号:
0701 ;
070101 ;
摘要:
We study the global properties of D-n, the Turing degrees of the n-r.e. sets. In Theorem 1.5, we show that the first order of D-n is not decidable. In Theorem 1.6, we show that for any two n and m with n < m, D-n is not a Sigma(1)-substructure of D-m.