98,409 research outputs found
Extensions of nominal terms
This thesis studies two major extensions of nominal terms. In particular, we
study an extension with -abstraction over nominal unknowns and atoms, and an
extension with an arguably better theory of freshness and -equivalence.
Nominal terms possess two levels of variable: atoms a represent variable symbols,
and unknowns X are `real' variables. As a syntax, they are designed to facilitate
metaprogramming; unknowns are used to program on syntax with variable symbols.
Originally, the role of nominal terms was interpreted narrowly. That is, they
were seen solely as a syntax for representing partially-speci ed abstract syntax with
binding.
The main motivation of this thesis is to extend nominal terms so that they can
be used for metaprogramming on proofs, programs, etc. and not just for metaprogramming
on abstract syntax with binding. We therefore extend nominal terms
in two signi cant ways: adding -abstraction over nominal unknowns and atoms|
facilitating functional programing|and improving the theory of -equivalence that
nominal terms possesses.
Neither of the two extensions considered are trivial. The capturing substitution
action of nominal unknowns implies that our notions of scope, intuited from working
with syntax possessing a non-capturing substitution, such as the -calculus, is no
longer applicable. As a result, notions of -abstraction and -equivalence must be
carefully reconsidered.
In particular, the rst research contribution of this thesis is the two-level -
calculus, intuitively an intertwined pair of -calculi. As the name suggests, the
two-level -calculus has two level of variable, modelled by nominal atoms and unknowns,
respectively. Both levels of variable can be -abstracted, and requisite
notions of -reduction are provided. The result is an expressive context-calculus.
The traditional problems of handling -equivalence and the failure of commutation
between instantiation and -reduction in context-calculi are handled through the
use of two distinct levels of variable, swappings, and freshness side-conditions on
unknowns, i.e. `nominal technology'.
The second research contribution of this thesis is permissive nominal terms,
an alternative form of nominal term. They retain the `nominal' rst-order
avour
of nominal terms (in fact, their grammars are almost identical) but forego the use
of explicit freshness contexts. Instead, permissive nominal terms label unknowns
with a permission sort, where permission sorts are in nite and coin nite sets of
atoms. This in nite-coin nite nature means that permissive nominal terms recover
two properties|we call them the `always-fresh' and `always-rename' properties
that nominal terms lack. We argue that these two properties bring the theory of
-equivalence on permissive nominal terms closer to `informal practice'.
The reader may consider -abstraction and -equivalence so familiar as to be
`solved problems'. The work embodied in this thesis stands testament to the fact
that this isn't the case. Considering -abstraction and -equivalence in the context
of two levels of variable poses some new and interesting problems and throws light
on some deep questions related to scope and binding
Priorities Without Priorities: Representing Preemption in Psi-Calculi
Psi-calculi is a parametric framework for extensions of the pi-calculus with
data terms and arbitrary logics. In this framework there is no direct way to
represent action priorities, where an action can execute only if all other
enabled actions have lower priority. We here demonstrate that the psi-calculi
parameters can be chosen such that the effect of action priorities can be
encoded.
To accomplish this we define an extension of psi-calculi with action
priorities, and show that for every calculus in the extended framework there is
a corresponding ordinary psi-calculus, without priorities, and a translation
between them that satisfies strong operational correspondence. This is a
significantly stronger result than for most encodings between process calculi
in the literature.
We also formally prove in Nominal Isabelle that the standard congruence and
structural laws about strong bisimulation hold in psi-calculi extended with
priorities.Comment: In Proceedings EXPRESS/SOS 2014, arXiv:1408.127
The controversial link between exchange rate volatility and exports: Evidence from Tunisian case
This paper tries to revisit the interaction between exchange uncertainty and exports in the Tunisian case. By using various GARCH extensions (i.e. Standard GARCH, Integrated GARCH, Exponential GARCH and Weighted GARCH) we show that the effect of exchange returns on changes in exports depends on time varying between low and high volatility in real terms (i.e. either structural breaks or shifts) and leverage effect (i.e. either good or bad news) in nominal terms. Our results also reveal that all considered links either in nominal or real terms are highly persistent, which means a great tendency to long memory process
The controversial link between exchange rate volatility and exports: Evidence from Tunisian case
This paper tries to revisit the interaction between exchange uncertainty and exports in the Tunisian case. By using various GARCH extensions (i.e. Standard GARCH, Integrated GARCH, Exponential GARCH and Weighted GARCH) we show that the effect of exchange returns on changes in exports depends on time varying between low and high volatility in real terms (i.e. either structural breaks or shifts) and leverage effect (i.e. either good or bad news) in nominal terms. Our results also reveal that all considered links either in nominal or real terms are highly persistent, which means a great tendency to long memory process
A dependent nominal type theory
Nominal abstract syntax is an approach to representing names and binding
pioneered by Gabbay and Pitts. So far nominal techniques have mostly been
studied using classical logic or model theory, not type theory. Nominal
extensions to simple, dependent and ML-like polymorphic languages have been
studied, but decidability and normalization results have only been established
for simple nominal type theories. We present a LF-style dependent type theory
extended with name-abstraction types, prove soundness and decidability of
beta-eta-equivalence checking, discuss adequacy and canonical forms via an
example, and discuss extensions such as dependently-typed recursion and
induction principles
Shape constrained additive models
A framework is presented for generalized additive modelling under shape constraints on the component functions of the linear predictor of the GAM. We represent shape constrained model components by mildly non-linear extensions of P-splines. Models can contain multiple shape constrained and unconstrained terms as well as shape constrained multi-dimensional smooths. The constraints considered are on the sign of the first or/and the second derivatives of the smooth terms. A key advantage of the approach is that it facilitates efficient estimation of smoothing parameters as an integral part of model estimation, via GCV or AIC, and numerically robust algorithms for this are presented. We also derive simulation free approximate Bayesian confidence intervals for the smooth components, which are shown to achieve close to nominal coverage probabilities. Applications are presented using real data examples including the risk of disease in relation to proximity to municipal incinerators and the association between air pollution and health
Constraint Handling Rules with Binders, Patterns and Generic Quantification
Constraint Handling Rules provide descriptions for constraint solvers.
However, they fall short when those constraints specify some binding structure,
like higher-rank types in a constraint-based type inference algorithm. In this
paper, the term syntax of constraints is replaced by -tree syntax, in
which binding is explicit; and a new generic quantifier is introduced,
which is used to create new fresh constants.Comment: Paper presented at the 33nd International Conference on Logic
Programming (ICLP 2017), Melbourne, Australia, August 28 to September 1, 2017
16 pages, LaTeX, no PDF figure
Supplement to "Structured additive regression for categorical space-time data: A mixed model approach"
This technical report acts as a supplement to the paper "Structured additive regression for categorical space-time data: A mixed model approach" (Kneib and Fahrmeir, Biometrics, 2005, to appear). Details on several specific models for categorical responses are given as well as a description on how to construct design matrices in structured additive regression models. Furthermore some technical information on inferential issues and additional results from the simulation studies are provided. To ease orientation, sections in the supplement are named in analogy to the sections in the original paper. Also, formulas are presented with the same numbers
Named Models in Coalgebraic Hybrid Logic
Hybrid logic extends modal logic with support for reasoning about individual
states, designated by so-called nominals. We study hybrid logic in the broad
context of coalgebraic semantics, where Kripke frames are replaced with
coalgebras for a given functor, thus covering a wide range of reasoning
principles including, e.g., probabilistic, graded, default, or coalitional
operators. Specifically, we establish generic criteria for a given coalgebraic
hybrid logic to admit named canonical models, with ensuing completeness proofs
for pure extensions on the one hand, and for an extended hybrid language with
local binding on the other. We instantiate our framework with a number of
examples. Notably, we prove completeness of graded hybrid logic with local
binding
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