6,707 research outputs found
Equivariant ZFA with Choice: a position paper
We propose Equivariant ZFA with Choice as a foundation for nominal techniques
that is stronger than ZFC and weaker than FM, and why this may be particularly
helpful in the context of automated reasoning.Comment: In ARW 201
The language of Stratified Sets is confluent and strongly normalising
We study the properties of the language of Stratified Sets (first-order logic
with and a stratification condition) as used in TST, TZT, and (with
stratifiability instead of stratification) in Quine's NF. We find that the
syntax forms a nominal algebra for substitution and that stratification and
stratifiability imply confluence and strong normalisation under rewrites
corresponding naturally to -conversion.Comment: arXiv admin note: text overlap with arXiv:1406.406
Consistency of Quine's New Foundations using nominal techniques
We build a model in nominal sets for TST+; typed set theory with typical
ambiguity. It is known that this is equivalent to the consistency of Quine's
New Foundations.
Nominal techniques are used to constrain the size of powersets and thus model
typical ambiguity
Semantics out of context: nominal absolute denotations for first-order logic and computation
Call a semantics for a language with variables absolute when variables map to
fixed entities in the denotation. That is, a semantics is absolute when the
denotation of a variable a is a copy of itself in the denotation. We give a
trio of lattice-based, sets-based, and algebraic absolute semantics to
first-order logic. Possibly open predicates are directly interpreted as lattice
elements / sets / algebra elements, subject to suitable interpretations of the
connectives and quantifiers. In particular, universal quantification "forall
a.phi" is interpreted using a new notion of "fresh-finite" limit and using a
novel dual to substitution.
The interest of this semantics is partly in the non-trivial and beautiful
technical details, which also offer certain advantages over existing
semantics---but also the fact that such semantics exist at all suggests a new
way of looking at variables and the foundations of logic and computation, which
may be well-suited to the demands of modern computer science
Representation and duality of the untyped lambda-calculus in nominal lattice and topological semantics, with a proof of topological completeness
We give a semantics for the lambda-calculus based on a topological duality
theorem in nominal sets. A novel interpretation of lambda is given in terms of
adjoints, and lambda-terms are interpreted absolutely as sets (no valuation is
necessary)
Closed nominal rewriting and efficiently computable nominal algebra equality
We analyse the relationship between nominal algebra and nominal rewriting,
giving a new and concise presentation of equational deduction in nominal
theories. With some new results, we characterise a subclass of equational
theories for which nominal rewriting provides a complete procedure to check
nominal algebra equality. This subclass includes specifications of the
lambda-calculus and first-order logic.Comment: In Proceedings LFMTP 2010, arXiv:1009.218
Systemization of Pluggable Transports for Censorship Resistance
An increasing number of countries implement Internet censorship at different
scales and for a variety of reasons. In particular, the link between the
censored client and entry point to the uncensored network is a frequent target
of censorship due to the ease with which a nation-state censor can control it.
A number of censorship resistance systems have been developed thus far to help
circumvent blocking on this link, which we refer to as link circumvention
systems (LCs). The variety and profusion of attack vectors available to a
censor has led to an arms race, leading to a dramatic speed of evolution of
LCs. Despite their inherent complexity and the breadth of work in this area,
there is no systematic way to evaluate link circumvention systems and compare
them against each other. In this paper, we (i) sketch an attack model to
comprehensively explore a censor's capabilities, (ii) present an abstract model
of a LC, a system that helps a censored client communicate with a server over
the Internet while resisting censorship, (iii) describe an evaluation stack
that underscores a layered approach to evaluate LCs, and (iv) systemize and
evaluate existing censorship resistance systems that provide link
circumvention. We highlight open challenges in the evaluation and development
of LCs and discuss possible mitigations.Comment: Content from this paper was published in Proceedings on Privacy
Enhancing Technologies (PoPETS), Volume 2016, Issue 4 (July 2016) as "SoK:
Making Sense of Censorship Resistance Systems" by Sheharbano Khattak, Tariq
Elahi, Laurent Simon, Colleen M. Swanson, Steven J. Murdoch and Ian Goldberg
(DOI 10.1515/popets-2016-0028
The retail of welfare-friendly products: A comparative assessment of the nature of the market for welfare-friendly products in six European Countries
This paper attempts to describe the market for welfare-friendly foodstuffs within larger retailing trends in six study countries in Europe (Norway, Sweden, Italy, France, the Netherlands and the UK). This is based on the findings to date from the work carried out by the work package 1.2 whose aims are to study the current and potential market for welfare-friendly foodstuffs. The aims of the current empirical stages of work package 1.2 are focussed on – what do retailers communicate to consumers about animal welfare? How is animal welfare framed? Are welfare-claims used on their own or within broader issues of quality
Finite and infinite support in nominal algebra and logic: nominal completeness theorems for free
By operations on models we show how to relate completeness with respect to
permissive-nominal models to completeness with respect to nominal models with
finite support. Models with finite support are a special case of
permissive-nominal models, so the construction hinges on generating from an
instance of the latter, some instance of the former in which sufficiently many
inequalities are preserved between elements. We do this using an infinite
generalisation of nominal atoms-abstraction.
The results are of interest in their own right, but also, we factor the
mathematics so as to maximise the chances that it could be used off-the-shelf
for other nominal reasoning systems too. Models with infinite support can be
easier to work with, so it is useful to have a semi-automatic theorem to
transfer results from classes of infinitely-supported nominal models to the
more restricted class of models with finite support.
In conclusion, we consider different permissive-nominal syntaxes and nominal
models and discuss how they relate to the results proved here
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