06055332

j

06055332 Baklanova, N.A. Minimal elements and minimal coverings in the Rogers semilattice of computable numberings in the hyperarithmetical hierarchy. Vestn. Novosib. Gos. Univ., Ser. Mat. Mekh. Inform. 11, No. 3, 77-84 (2011). 2011 Novosibirskij Gosuniversitet, Novosibirsk RU numbering Rogers semilattice hyperarithmetical hierarchy minimal element minimal cover Summary: We prove that the Rogers semilattice of any infinite $\Sigma_\omega$-computable family contains infinitely many minimal elements and each non-$0'$-universal numbering has infinitely many minimal covers.