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SUMMARY:Nikolai Bazhenov (Sobolev Institute of Mathematics)
DTSTART:20200609T140000Z
DTEND:20200609T150000Z
DTSTAMP:20260423T024534Z
UID:CTA/8
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/CTA/8/">Roge
 rs semilattices in the analytical hierarchy</a>\nby Nikolai Bazhenov (Sobo
 lev Institute of Mathematics) as part of Computability theory and applicat
 ions\n\n\nAbstract\nFor a countable set S\, a numbering of S is a surjecti
 ve map from ω onto S. A numbering ν is reducible to a numbering μ if th
 ere is a computable function f such that ν(x) = μ f(x) for all indices x
 . The notion of reducibility between numberings gives rise to a class of u
 pper semilattices\, which are usually called Rogers semilattices. We discu
 ss recent results on Rogers semilattices induced by numberings in the anal
 ytical hierarchy. Special attention is given to the first-order properties
  of Rogers semilattices. The talk is based on joint works with Manat Musta
 fa\, Sergei Ospichev\, and Mars Yamaleev.\n
LOCATION:https://researchseminars.org/talk/CTA/8/
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