744 research outputs found
Some results on ordered structures in toposes
A topos version of Cantorâs back and forth theorem is established and used to prove that the ordered structure of the rational numbers (Q, \u3c) is homogeneous in any topos with natural numbers object. The notion of effective homogeneity is introduced, and it is shown that (Q, \u3c) is a minimal effectively homogeneous structure, that is, it can be embedded in every other effectively homogeneous ordered structure
Models of Type Theory Based on Moore Paths
This paper introduces a new family of models of intensional Martin-L\"of type
theory. We use constructive ordered algebra in toposes. Identity types in the
models are given by a notion of Moore path. By considering a particular gros
topos, we show that there is such a model that is non-truncated, i.e. contains
non-trivial structure at all dimensions. In other words, in this model a type
in a nested sequence of identity types can contain more than one element, no
matter how great the degree of nesting. Although inspired by existing
non-truncated models of type theory based on simplicial and cubical sets, the
notion of model presented here is notable for avoiding any form of Kan filling
condition in the semantics of types.Comment: This is a revised and expanded version of a paper with the same name
that appeared in the proceedings of the 2nd International Conference on
Formal Structures for Computation and Deduction (FSCD 2017
Bohrification
New foundations for quantum logic and quantum spaces are constructed by
merging algebraic quantum theory and topos theory. Interpreting Bohr's
"doctrine of classical concepts" mathematically, given a quantum theory
described by a noncommutative C*-algebra A, we construct a topos T(A), which
contains the "Bohrification" B of A as an internal commutative C*-algebra. Then
B has a spectrum, a locale internal to T(A), the external description S(A) of
which we interpret as the "Bohrified" phase space of the physical system. As in
classical physics, the open subsets of S(A) correspond to (atomic)
propositions, so that the "Bohrified" quantum logic of A is given by the
Heyting algebra structure of S(A). The key difference between this logic and
its classical counterpart is that the former does not satisfy the law of the
excluded middle, and hence is intuitionistic. When A contains sufficiently many
projections (e.g. when A is a von Neumann algebra, or, more generally, a
Rickart C*-algebra), the intuitionistic quantum logic S(A) of A may also be
compared with the traditional quantum logic, i.e. the orthomodular lattice of
projections in A. This time, the main difference is that the former is
distributive (even when A is noncommutative), while the latter is not.
This chapter is a streamlined synthesis of 0709.4364, 0902.3201, 0905.2275.Comment: 44 pages; a chapter of the first author's PhD thesis, to appear in
"Deep Beauty" (ed. H. Halvorson
Characterizations of categories of commutative C*-subalgebras
We aim to characterize the category of injective *-homomorphisms between
commutative C*-subalgebras of a given C*-algebra A. We reduce this problem to
finding a weakly terminal commutative subalgebra of A, and solve the latter for
various C*-algebras, including all commutative ones and all type I von Neumann
algebras. This addresses a natural generalization of the Mackey-Piron
programme: which lattices are those of closed subspaces of Hilbert space? We
also discuss the way this categorified generalization differs from the original
question.Comment: 24 page
A representation theorem for integral rigs and its applications to residuated lattices
We prove that every integral rig in Sets is (functorially) the rig of global
sections of a sheaf of really local integral rigs. We also show that this
representation result may be lifted to residuated integral rigs and then
restricted to varieties of these. In particular, as a corollary, we obtain a
representation theorem for pre-linear residuated join-semilattices in terms of
totally ordered fibers. The restriction of this result to the level of
MV-algebras coincides with the Dubuc-Poveda representation theorem.Comment: Manuscript submitted for publicatio
Totally distributive toposes
A locally small category E is totally distributive (as defined by
Rosebrugh-Wood) if there exists a string of adjoint functors t -| c -| y, where
y : E --> E^ is the Yoneda embedding. Saying that E is lex totally distributive
if, moreover, the left adjoint t preserves finite limits, we show that the lex
totally distributive categories with a small set of generators are exactly the
injective Grothendieck toposes, studied by Johnstone and Joyal. We characterize
the totally distributive categories with a small set of generators as exactly
the essential subtoposes of presheaf toposes, studied by Kelly-Lawvere and
Kennett-Riehl-Roy-Zaks.Comment: Now includes extended result: The lex totally distributive categories
with a small set of generators are exactly the injective Grothendieck
toposes; Made changes to abstract and intro to reflect the enhanced result;
Changed formatting of diagram
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