512 research outputs found
An interactive semantics of logic programming
We apply to logic programming some recently emerging ideas from the field of
reduction-based communicating systems, with the aim of giving evidence of the
hidden interactions and the coordination mechanisms that rule the operational
machinery of such a programming paradigm. The semantic framework we have chosen
for presenting our results is tile logic, which has the advantage of allowing a
uniform treatment of goals and observations and of applying abstract
categorical tools for proving the results. As main contributions, we mention
the finitary presentation of abstract unification, and a concurrent and
coordinated abstract semantics consistent with the most common semantics of
logic programming. Moreover, the compositionality of the tile semantics is
guaranteed by standard results, as it reduces to check that the tile systems
associated to logic programs enjoy the tile decomposition property. An
extension of the approach for handling constraint systems is also discussed.Comment: 42 pages, 24 figure, 3 tables, to appear in the CUP journal of Theory
and Practice of Logic Programmin
Interacting Hopf Algebras
We introduce the theory IH of interacting Hopf algebras, parametrised over a
principal ideal domain R. The axioms of IH are derived using Lack's approach to
composing PROPs: they feature two Hopf algebra and two Frobenius algebra
structures on four different monoid-comonoid pairs. This construction is
instrumental in showing that IH is isomorphic to the PROP of linear relations
(i.e. subspaces) over the field of fractions of R
A unified framework for generalized multicategories
Notions of generalized multicategory have been defined in numerous contexts
throughout the literature, and include such diverse examples as symmetric
multicategories, globular operads, Lawvere theories, and topological spaces. In
each case, generalized multicategories are defined as the "lax algebras" or
"Kleisli monoids" relative to a "monad" on a bicategory. However, the meanings
of these words differ from author to author, as do the specific bicategories
considered. We propose a unified framework: by working with monads on double
categories and related structures (rather than bicategories), one can define
generalized multicategories in a way that unifies all previous examples, while
at the same time simplifying and clarifying much of the theory.Comment: 76 pages; final version, to appear in TA
Free-algebra functors from a coalgebraic perspective
Given a set of equations, the free-algebra functor
associates to each set of variables the free algebra over
. Extending the notion of \emph{derivative} for an arbitrary set
of equations, originally defined by Dent, Kearnes, and Szendrei, we
show that preserves preimages if and only if , i.e. derives its derivative . If weakly
preserves kernel pairs, then every equation gives rise to a
term such that and . In
this case n-permutable varieties must already be permutable, i.e. Mal'cev.
Conversely, if defines a Mal'cev variety, then weakly
preserves kernel pairs. As a tool, we prove that arbitrary endofunctors
weakly preserve kernel pairs if and only if they weakly preserve pullbacks
of epis
Constructing categories and setoids of setoids in type theory
In this paper we consider the problem of building rich categories of setoids,
in standard intensional Martin-L\"of type theory (MLTT), and in particular how
to handle the problem of equality on objects in this context. Any
(proof-irrelevant) family F of setoids over a setoid A gives rise to a category
C(A, F) of setoids with objects A. We may regard the family F as a setoid of
setoids, and a crucial issue in this article is to construct rich or large
enough such families. Depending on closure conditions of F, the category C(A,
F) has corresponding categorical constructions. We exemplify this with finite
limits. A very large family F may be obtained from Aczel's model construction
of CZF in type theory. It is proved that the category so obtained is isomorphic
to the internal category of sets in this model. Set theory can thus establish
(categorical) properties of C(A, F) which may be used in type theory. We also
show that Aczel's model construction may be extended to include the elements of
any setoid as atoms or urelements. As a byproduct we obtain a natural extension
of CZF, adding atoms. This extension, CZFU, is validated by the extended model.
The main theorems of the paper have been checked in the proof assistant Coq
which is based on MLTT. A possible application of this development is to
integrate set-theoretic and type-theoretic reasoning in proof assistants.Comment: 14 page
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