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VERSION:2.0
METHOD:PUBLISH
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LOCATION:60 Evans Hall
SEQUENCE:0
DTEND:20091009T180000
DTSTART:20091009T161000
UID:philosophy.berkeley.edu:events:581
DTSTAMP:20091124T192343
DESCRIPTION:We will show there is a topological space for which presheaves 
 are the same thing as trees. We will further show that there is a sheaf on 
 this topological space which has an important relationship with Baire space
 .  We will then use these connections to show how a definition by transfini
 te recursion can be thought of as an operation on sheaves\, and how the wel
 l-definedness of such a definition can be thought of as a property of the s
 heaf we are working on.  This will then allow us to define a second-order t
 ree as a sheaf on a tree and to expand our notion of definition by transfin
 ite recursion to all well-founded second-order trees (even those which are 
 ill-founded as normal trees).  We will then mention how these techniques ca
 n be used to prove a variant of the Suslin-Kleene Separation theorem.\n
SUMMARY:Logic Colloquium\nNate Ackerman\nTrees\, Sheaves\, and Definition b
 y Recursion
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