## Abstract

We settle a series of questions first raised by Yates at the Jerusalem (1968) Colloquium on Mathematical Logic by characterizing the initial segments of the degrees of unsolvability of size א_{1}: Every upper semi-lattice of size א_{1} with zero, in which every element has at most countably many predecessors, is isomorphic to an initial segment of the Turing degrees.

Original language | English |
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Pages (from-to) | 1-51 |

Number of pages | 51 |

Journal | Israel Journal of Mathematics |

Volume | 53 |

Issue number | 1 |

DOIs | |

State | Published - 1 Feb 1986 |

## ASJC Scopus subject areas

- Mathematics (all)

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