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SUMMARY:Perfect toposes and infinitesimal weak generation - Peter Johnston
 e (DPMMS)
DTSTART:20180206T141500Z
DTEND:20180206T151500Z
UID:TALK100093@talks.cam.ac.uk
CONTACT:Tamara von Glehn
DESCRIPTION:In his 2007 paper on axiomatic cohesion\, Bill Lawvere\nintrod
 uced a notion of `weak generation' of a topos by\na family of objects\, wh
 ich has not been much investigated\nuntil recently. Last year Matias Menni
  showed that every\nsufficiently coherent topos (in Lawvere's sense) is we
 akly\ngenerated by objects which are `infinitesimal' in the sense\nthat th
 ey are not-not-singletons. We show that weak generation\nby infinitesimals
  is equivalent to a much simpler (and older)\nnotion\, that of being perfe
 ct\, which arose out of Peter\nFreyd's work on the Cantor coderivative.
LOCATION:MR5\, Centre for Mathematical Sciences
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