Peter F: For that we need -- as we called it in Cats and Alligators -- Wilson space.
What section number? (Not in the index.)
Actually, not the space but the linearly ordered set, most easily defined as the lexicographically ordered subset, W, of sequences with values in {-1, 0, 1} consisting of all those sequences such that for all n a(n) = 0 => a(n+1) = 0 (take a finite word on {-1,1} and pad it out to an infinite sequence by tacking on 0s).
(The parenthetical explanation presumably is meant to apply only to those words containing at least one 0, i.e. W should also contain the infinite words on {-1,1} (else it would be countable).) So shouldn't it be called the Wilson chain then, rather than Wilson space? Ditto for the turkey chain I described yesterday (rationals in quadruplicate, vs. triplicate for the Wilson chain). As a topological space, I don't understand what Wilson space is. The order interval topology (generated by the open order intervals, sets of the form {x | p<x<q}) on a chain makes the irrationals Baire space, the reals the continuum, and the-reals-with-each-rational-duplicated Cantor space. If I haven't miscalculated, it makes the Wilson chain simply C+N, the sum of Cantor space and discrete N (natural numbers). (N arises as the middle rational in each triple. Each middle rational appears simultaneously as the greatest element of one open interval and the least element of another; intersect those to get a singleton open.) If Wilson space is not the order interval topology, i.e. not C+N, then surely it must not be Hausdorff. The only natural possibility I could think of in that case is the 1-point compactification of C iterated omega times, i.e. each element of N appears only in cofinite opens, which didn't seem likely. In any of these cases, my analogously defined "turkey space" looks like it ought to be homeomorphic to Wilson space. Vaughan 28-Nov-2004 13:37:05 -0400,5008;000000000000-00000000
Vaughan points out that Wilson space didn't make it into the index of Cats & Allegators. Whoops. It's to be found in section 1.749, page 129 (but not in small caps, which, I guess, is how it was missed when preparing the index). It is not an order-interval topology. Indeed, it is not Hausdorf. As I remarked in my last post, Wilson space is definable as the final co-algebra of the functor on Top that sends X to the scone of X + X. (The only Hausdorf scone is the scone of the empty set.) Its important properties are two: 1) the category of sheaves on Wilson space is equivalent to the category of pre-sheaves on the infinite binary tree (viewed as a poset with the root as top); and, 2) there's an open continuous map from the closed interval onto Wilson space (hence from any reasonable locally euclidean space). All of which yields a completeness theorem for intuitionistic first-order logic with respect to the semantics of sheaves on the reals (or any reasonable locally euclidean space). 29-Nov-2004 11:21:44 -0400,6038;000000000000-00000000
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Vaughan Pratt