For more information about this meeting, contact Stephen Simpson, Jan Reimann.

Title: | Implicit definability in arithmetic, part 3. |

Seminar: | Logic Seminar |

Speaker: | Stephen G. Simpson, Pennsylvania State University |

Abstract: |

In this talk I present a new proof of Harrington's theorems concerning implicit definability over the integers. Unlike previous proofs, the new proof is easy and does not involve priority arguments. The theorems read as follows. (1) There exist two sets of integers, each of which is implictly definable yet neither of which is explicitly definable from the other. (2) There exists a set of integers which belongs to an implicitly definable countable set of sets but is not by itself implicitly definable. |

### Room Reservation Information

Room Number: | MB315 |

Date: | 04 / 02 / 2013 |

Time: | 02:30pm - 03:45pm |