Preprint : Ultrasheaves and double negation

Hello, The following preprint is available. Comments are welcome. Title : Ultrasheaves and double negation Authors : Steve Awodey and Jonas Eliasson Abstract : Moerdijk has introduced a topos of sheaves on a category of filters. Following his suggestion, we prove that its double negation subtopos is the topos of sheaves on the subcategory of ultrafilters - the \emph{ultrasheaves}. We then use this result to establish a double negation translation of results between the topos of ultrasheaves and the topos on filters. Url : http://www.math.uu.se/~jonase/research.html (available both as .ps and .pdf) /Jonas Eliasson 19-Nov-2002 19:41:21 -0400,5013;000000000000-00000000