98 research outputs found
Initial Semantics for Strengthened Signatures
We give a new general definition of arity, yielding the companion notions of
signature and associated syntax. This setting is modular in the sense requested
by Ghani and Uustalu: merging two extensions of syntax corresponds to building
an amalgamated sum. These signatures are too general in the sense that we are
not able to prove the existence of an associated syntax in this general
context. So we have to select arities and signatures for which there exists the
desired initial monad. For this, we follow a track opened by Matthes and
Uustalu: we introduce a notion of strengthened arity and prove that the
corresponding signatures have initial semantics (i.e. associated syntax). Our
strengthened arities admit colimits, which allows the treatment of the
\lambda-calculus with explicit substitution.Comment: In Proceedings FICS 2012, arXiv:1202.317
An Extension of Models of Axiomatic Domain Theory to Models of Synthetic Domain Theory
We relate certain models of Axiomatic Domain Theory (ADT)
and Synthetic Domain Theory (SDT). On the one hand, we introduce
a class of non-elementary models of SDT and show that the domains in
them yield models of ADT. On the other hand, for each model of ADT
in a wide class we construct a model of SDT such that the domains in
it provide a model of ADT which conservatively extends the original
model
An Axiomatisation of Computationally Adequate Domain Theoretic Models of FPC
Categorical models of the metalanguage FPC (a
type theory with sums, products, exponentials and
recursive types) are defined. Then, domain-theoretic
models of FPC are axiomatised and a wide subclass of
them —the non-trivial and absolute ones— are proved
to be both computationally sound and adequate.
Examples include: the category of cpos and partial
continuous functions and functor categories over it
Abstract Syntax and Variable Binding (Extended Abstract)
We develop a theory of abstract syntax with variable
binding. To every binding signature we associate a category
of models consisting of variable sets endowed with
compatible algebra and substitution structures. The syntax
generated by the signature is the initial model. This gives a
notion of initial algebra semantics encompassing the traditional
one; besides compositionality, it automatically veri-
fies the semantic substitution lemma
Innocent strategies as presheaves and interactive equivalences for CCS
Seeking a general framework for reasoning about and comparing programming
languages, we derive a new view of Milner's CCS. We construct a category E of
plays, and a subcategory V of views. We argue that presheaves on V adequately
represent innocent strategies, in the sense of game semantics. We then equip
innocent strategies with a simple notion of interaction. This results in an
interpretation of CCS.
Based on this, we propose a notion of interactive equivalence for innocent
strategies, which is close in spirit to Beffara's interpretation of testing
equivalences in concurrency theory. In this framework we prove that the
analogues of fair and must testing equivalences coincide, while they differ in
the standard setting.Comment: In Proceedings ICE 2011, arXiv:1108.014
Interaction and observation, categorically
This paper proposes to use dialgebras to specify the semantics of interactive
systems in a natural way. Dialgebras are a conservative extension of
coalgebras. In this categorical model, from the point of view that we provide,
the notions of observation and interaction are separate features. This is
useful, for example, in the specification of process equivalences, which are
obtained as kernels of the homomorphisms of dialgebras. As an example we
present the asynchronous semantics of the CCS.Comment: In Proceedings ICE 2011, arXiv:1108.014
Nominal Henkin Semantics: simply-typed lambda-calculus models in nominal sets
We investigate a class of nominal algebraic Henkin-style models for the
simply typed lambda-calculus in which variables map to names in the denotation
and lambda-abstraction maps to a (non-functional) name-abstraction operation.
The resulting denotations are smaller and better-behaved, in ways we make
precise, than functional valuation-based models.
Using these new models, we then develop a generalisation of \lambda-term
syntax enriching them with existential meta-variables, thus yielding a theory
of incomplete functions. This incompleteness is orthogonal to the usual notion
of incompleteness given by function abstraction and application, and
corresponds to holes and incomplete objects.Comment: In Proceedings LFMTP 2011, arXiv:1110.668
Bindings as bounded natural functors
We present a general framework for specifying and reasoning about syntax with bindings. Abstract binder types are modeled using a universe of functors on sets, subject to a number of operations that can be used to construct complex binding patterns and binding-aware datatypes, including non-well-founded and infinitely branching types, in a modular fashion. Despite not committing to any syntactic format, the framework is “concrete” enough to provide definitions of the fundamental operators on terms (free variables, alpha-equivalence, and capture-avoiding substitution) and reasoning and definition principles. This work is compatible with classical higher-order logic and has been formalized in the proof assistant Isabelle/HOL
Estimating the global conservation status of more than 15,000 Amazonian tree species
Estimates of extinction risk for Amazonian plant and animal species are rare and not often incorporated into land-use policy and conservation planning. We overlay spatial distribution models with historical and projected deforestation to show that at least 36% and up to 57% of all Amazonian tree species are likely to qualify as globally threatened under International Union for Conservation of Nature (IUCN) Red List criteria. If confirmed, these results would increase the number of threatened plant species on Earth by 22%. We show that the trends observed in Amazonia apply to trees throughout the tropics, and we predict thatmost of the world’s >40,000 tropical tree species now qualify as globally threatened. A gap analysis suggests that existing Amazonian protected areas and indigenous territories will protect viable populations of most threatened species if these areas suffer no further degradation, highlighting the key roles that protected areas, indigenous peoples, and improved governance can play in preventing large-scale extinctions in the tropics in this century
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