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DTSTART:20170312T070000
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DTSTART:20161106T060000
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DTSTART;TZID=America/Toronto:20170411T153000
SEQUENCE:0
TRANSP:TRANSPARENT
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URL:https://uwaterloo.ca/pure-mathematics/events/computability-learning-sem
 inar-66
SUMMARY:Computability Learning Seminar
CLASS:PUBLIC
DESCRIPTION:JONNY STEPHENSON\, DEPARTMENT OF PURE MATHEMATICS\, UNIVERSITY 
 OF\nWATERLOO\n\n\"Degree Spectra\"\n\nLast week we saw that every countabl
 e ideal in the enumeration degrees\nis the co-spectrum of some structure. 
 Now we will consider what sets\nof degrees are spectra of structures. We w
 ill see that the situation\nis quite different\, and that there are a numb
 er of classes which\ncannot be the spectrum of any structure. In particula
 r\, no nontrivial\ncountable union of enumeration upper cones can be the s
 pectrum of any\nstructure.\n\nMC 5403
DTSTAMP:20260607T130858Z
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