Degrees Joining to $0'$
Posner, David B. ; Robinson, Robert W.
J. Symbolic Logic, Tome 46 (1981) no. 1, p. 714-722 / Harvested from Project Euclid
It is shown that if $\mathscr{A}$ and $\mathscr{C}$ are sets of degrees uniformly recursive in $\mathbf{0}'$ with $\mathbf{0} \nonin \mathscr{C}$ then there is a degree $\mathbf{b}$ with $\mathbf{b}' = \mathbf{0}', \mathbf{b} \cup \mathbf{c} = \mathbf{0}'$ for every $c \in \mathscr{C}$, and $\mathbf{a} \nleq \mathbf{b}$ for every $\mathbf{a} \in \mathscr{A} \sim \{0\}$. The proof is given as an oracle construction recursive in $\mathbf{0}'$. It follows that any nonrecursive degree below $\mathbf{0}'$ can be joined to $\mathbf{0}'$ by a degree strictly below $\mathbf{0}'$. Also, if $\mathbf{a < 0}$' and $\mathbf{a}'' = \mathbf{0}''$ then there is a degree $\mathbf{b}$ such that $\mathbf{a} \cup \mathbf{b} = \mathbf{0}'$ and $\mathbf{a} \cap \mathbf{b} = \mathbf{0}$.
Publié le : 1981-12-14
Classification: 
@article{1183740882,
     author = {Posner, David B. and Robinson, Robert W.},
     title = {Degrees Joining to $0'$},
     journal = {J. Symbolic Logic},
     volume = {46},
     number = {1},
     year = {1981},
     pages = { 714-722},
     language = {en},
     url = {http://dml.mathdoc.fr/item/1183740882}
}
Posner, David B.; Robinson, Robert W. Degrees Joining to $0'$. J. Symbolic Logic, Tome 46 (1981) no. 1, pp.  714-722. http://gdmltest.u-ga.fr/item/1183740882/