487 research outputs found
Admissibility via Natural Dualities
It is shown that admissible clauses and quasi-identities of quasivarieties
generated by a single finite algebra, or equivalently, the quasiequational and
universal theories of their free algebras on countably infinitely many
generators, may be characterized using natural dualities. In particular,
axiomatizations are obtained for the admissible clauses and quasi-identities of
bounded distributive lattices, Stone algebras, Kleene algebras and lattices,
and De Morgan algebras and lattices.Comment: 22 pages; 3 figure
Sound and complete axiomatizations of coalgebraic language equivalence
Coalgebras provide a uniform framework to study dynamical systems, including
several types of automata. In this paper, we make use of the coalgebraic view
on systems to investigate, in a uniform way, under which conditions calculi
that are sound and complete with respect to behavioral equivalence can be
extended to a coarser coalgebraic language equivalence, which arises from a
generalised powerset construction that determinises coalgebras. We show that
soundness and completeness are established by proving that expressions modulo
axioms of a calculus form the rational fixpoint of the given type functor. Our
main result is that the rational fixpoint of the functor , where is a
monad describing the branching of the systems (e.g. non-determinism, weights,
probability etc.), has as a quotient the rational fixpoint of the
"determinised" type functor , a lifting of to the category of
-algebras. We apply our framework to the concrete example of weighted
automata, for which we present a new sound and complete calculus for weighted
language equivalence. As a special case, we obtain non-deterministic automata,
where we recover Rabinovich's sound and complete calculus for language
equivalence.Comment: Corrected version of published journal articl
Comparing theories: the dynamics of changing vocabulary. A case-study in relativity theory
There are several first-order logic (FOL) axiomatizations of special
relativity theory in the literature, all looking essentially different but
claiming to axiomatize the same physical theory. In this paper, we elaborate a
comparison, in the framework of mathematical logic, between these FOL theories
for special relativity. For this comparison, we use a version of mathematical
definability theory in which new entities can also be defined besides new
relations over already available entities. In particular, we build an
interpretation of the reference-frame oriented theory SpecRel into the
observationally oriented Signalling theory of James Ax. This interpretation
provides SpecRel with an operational/experimental semantics. Then we make
precise, "quantitative" comparisons between these two theories via using the
notion of definitional equivalence. This is an application of logic to the
philosophy of science and physics in the spirit of Johan van Benthem's work.Comment: 27 pages, 8 figures. To appear in Springer Book series Trends in
Logi
On the geometric theory of local MV-algebras
We investigate the geometric theory of local MV-algebras and its quotients
axiomatizing the local MV-algebras in a given proper variety of MV-algebras. We
show that, whilst the theory of local MV-algebras is not of presheaf type, each
of these quotients is a theory of presheaf type which is Morita-equivalent to
an expansion of the theory of lattice-ordered abelian groups. Di
Nola-Lettieri's equivalence is recovered from the Morita-equivalence for the
quotient axiomatizing the local MV-algebras in Chang's variety, that is, the
perfect MV-algebras. We establish along the way a number of results of
independent interest, including a constructive treatment of the radical for
MV-algebras in a fixed proper variety of MV-algebras and a representation
theorem for the finitely presentable algebras in such a variety as finite
products of local MV-algebras.Comment: 52 page
Abstract representation theory of Dynkin quivers of type A
We study the representation theory of Dynkin quivers of type A in abstract
stable homotopy theories, including those associated to fields, rings, schemes,
differential-graded algebras, and ring spectra. Reflection functors, (partial)
Coxeter functors, and Serre functors are defined in this generality and these
equivalences are shown to be induced by universal tilting modules, certain
explicitly constructed spectral bimodules. In fact, these universal tilting
modules are spectral refinements of classical tilting complexes. As a
consequence we obtain split epimorphisms from the spectral Picard groupoid to
derived Picard groupoids over arbitrary fields.
These results are consequences of a more general calculus of spectral
bimodules and admissible morphisms of stable derivators. As further
applications of this calculus we obtain examples of universal tilting modules
which are new even in the context of representations over a field. This
includes Yoneda bimodules on mesh categories which encode all the other
universal tilting modules and which lead to a spectral Serre duality result.
Finally, using abstract representation theory of linearly oriented
-quivers, we construct canonical higher triangulations in stable
derivators and hence, a posteriori, in stable model categories and stable
-categories
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