1,962 research outputs found
Models of Non-Well-Founded Sets via an Indexed Final Coalgebra Theorem
The paper uses the formalism of indexed categories to recover the proof of a
standard final coalgebra theorem, thus showing existence of final coalgebras
for a special class of functors on categories with finite limits and colimits.
As an instance of this result, we build the final coalgebra for the powerclass
functor, in the context of a Heyting pretopos with a class of small maps. This
is then proved to provide a model for various non-well-founded set theories,
depending on the chosen axiomatisation for the class of small maps
Multiplicative structure in equivariant cohomology
We introduce the notion of a strongly homotopy-comultiplicative resolution of
a module coalgebra over a chain Hopf algebra, which we apply to proving a
comultiplicative enrichment of a well-known theorem of Moore concerning the
homology of quotient spaces of group actions. The importance of our enriched
version of Moore's theorem lies in its application to the construction of
useful cochain algebra models for computing multiplicative structure in
equivariant cohomology.
In the special cases of homotopy orbits of circle actions on spaces and of
group actions on simplicial sets, we obtain small, explicit cochain algebra
models that we describe in detail.Comment: 28 pages. Final version (cosmetic changes, slight reorganization), to
appear in JPA
Well-Pointed Coalgebras
For endofunctors of varieties preserving intersections, a new description of
the final coalgebra and the initial algebra is presented: the former consists
of all well-pointed coalgebras. These are the pointed coalgebras having no
proper subobject and no proper quotient. The initial algebra consists of all
well-pointed coalgebras that are well-founded in the sense of Osius and Taylor.
And initial algebras are precisely the final well-founded coalgebras. Finally,
the initial iterative algebra consists of all finite well-pointed coalgebras.
Numerous examples are discussed e.g. automata, graphs, and labeled transition
systems
The homotopy theory of bialgebras over pairs of operads
We endow the category of bialgebras over a pair of operads in distribution
with a cofibrantly generated model category structure. We work in the category
of chain complexes over a field of characteristic zero. We split our
construction in two steps. In the first step, we equip coalgebras over an
operad with a cofibrantly generated model category structure. In the second one
we use the adjunction between bialgebras and coalgebras via the free algebra
functor. This result allows us to do classical homotopical algebra in various
categories such as associative bialgebras, Lie bialgebras or Poisson bialgebras
in chain complexes.Comment: 27 pages, final version, to appear in the Journal of Pure and Applied
Algebr
Coalgebraic Behavioral Metrics
We study different behavioral metrics, such as those arising from both
branching and linear-time semantics, in a coalgebraic setting. Given a
coalgebra for a functor , we define a framework for deriving pseudometrics on which
measure the behavioral distance of states.
A crucial step is the lifting of the functor on to a
functor on the category of pseudometric spaces.
We present two different approaches which can be viewed as generalizations of
the Kantorovich and Wasserstein pseudometrics for probability measures. We show
that the pseudometrics provided by the two approaches coincide on several
natural examples, but in general they differ.
If has a final coalgebra, every lifting yields in a
canonical way a behavioral distance which is usually branching-time, i.e., it
generalizes bisimilarity. In order to model linear-time metrics (generalizing
trace equivalences), we show sufficient conditions for lifting distributive
laws and monads. These results enable us to employ the generalized powerset
construction
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