Abstracts
Dec 11 2008, 10:30
Speaker: Carsten Schuermann
Title: Celf: An implementation of the concurrent logical framework CLF.
Abstract:
CLF (Concurrent LF) is a logical framework for specifying
and implementing deductive and concurrent systems from areas, such
as programming language theory, security protocol analysis, process algebras,
and logics. Celf is an implementation of the CLF type theory that
extends the LF type theory by linear types to support representation of
state and a monad to support representation of concurrency.
In my talk I will give a gentle introduction to the CLF type theory and
demo the type inference and logic programming features of the Celf system.
Dec 02 2008, 14:30
Speaker: Romain Beauxis and David Baelde
Title: Focusing in the asynchronous picalculus
Abstract:
During the asynchronous parallel execution of two concurrent programs, the
executions of each program are interleaved. This means that if the first
program has three steps to do during its execution, and the other two, then
all the possible combinations might be observed, so that an explicit
exploration of all possible executions of the two program in parallel has a
very important complexity.
A similar issue was already raised in linear logic, leading to the definition
of a certain category of focalised executions. Such executions constraints
the evaluation of the two programs so that all the executions of the first
one are done before it starts to execute the transitions of the second. It is
then proved, in linear logic, that the proof search is not weakened, while
the complexity of the search is greatly reduced.
The work presented here propose a transposition of this technique to the
asynchronous picalculus. Hence, we define the notion of focalised
transitions for the asynchronous picalculus, allowing to greatly reduce the
complixity of the evaluation of a process. Furthermore, we prove that
we preserve all the available information on the processes while using
focalised transitions.
Nov 04 2008, 14:30
Speaker: Alessio Guglielmi (University of Bath and INRIA Nancy GrandEst)
Title: Proof Identity, Proof Complexity and Deep Inference
Abstract:
We have been dealing with mathematical proofs for millennia, but we still don't know them enough to answer elementary questions, such as: `When are two proofs identical?' and `How complex need proofs be?' These questions correspond to open problems at the crossing of logic and computer science: respectively, the socalled `Hilbert's 24th problem' and `coNP vs NP'.
To deal with proof identity, we need new proof systems with a much improved ability to see the fine detail of proofs, i.e., we need systems whose inference rules only deal with a minimal amount of information. These rules are called `local' and cannot be obtained in the traditional proof theory. However, locality is achievable by adopting a relatively novel approach to the structure of proofs, that we call `deep inference'. Thanks to locality, not only are we able to see more detail, we are also able to discard unnecessary detail, the socalled `bureaucracy' of traditional proof systems. In particular, we can show that normalisation can be achieved in a largely syntaxindependent way by removing bureaucracy from deepinference proofs, and reducing them to their `atomic flow'.
We are about to satisfactorily solve the proof identity problem, by a coordinated effort involving several research groups. We have also made progress towards reducing the complexity of proofs and of their normalisation.
I will give an accessible survey of these topics, for anybody with an interest in the theoretical foundations of computer science. More on deep inference at http://alessio.guglielmi.name/res/cos.
Oct 21 2008, 11:00
Speaker: Stefan Hetzl
Title: On the nonconfluence of cutelimination
Abstract:
Cutelimination is one of the most important proof transformations in logic.
Historically, it has been introduced by Gentzen as a tool for consistency proofs
in the tradition of Hilbert's programme. It has however found many other
applications: One of them is the application of cutelimination to the analysis
of concrete mathematical proofs ('proof mining'). A famous example is Girard's
demonstration that from the topological FuerstenbergWeiss proof of
van der Waerden's theorem, the original combinatorial proof can be obtained.
However, cutelimination is an inherently nondeterministic process. At each
stage one has the choice between different cuts to reduce and  for a single
cut  there are different ways of reducing it. It is not clear, in how far this
formal nondeterminism may lead to mathematical differences in the resulting
elementary proofs. Understanding the possible span of the results of
cutelimination procedures is of fundamental importance for judging proof
analyses based on these methods.
In this talk I will treat the standard syntactic cutelimination for firstorder
classical logic and report on a recent result obtained jointly with M. Baaz on
the nonconfluence of this reduction: It is possible to construct a sequence of
polynomialsize proofs s.t. a proof in this sequence has nonelementarily many
different cutfree normal forms (each of nonelementary size). These normal
forms are different in a strong sense: They not only represent different
Herbranddisjunctions but also have different propositional structures and hence
are not substitutioninstances of a single general proof.
This result shows that the constructive content of a cutfree proof does not
only depend on the proof with cuts from which it was generated but also on the
way the cuts are eliminated.
Oct 03 2008, 14:30
Speaker: Stefan Haar
Title: Partial Orders are good for you !
Abstract:
The talk takes a stand to advocate the use of Petri nettype models and partial order unfolding semantics for the analysis of large networked systems, exemplified by fault diagnosis in telecommunication networks. The methodology of asynchronous diagnosis is presented, followed by a discussion of related problems that are fun but challenging, such as probabilistic processes, distribution of unfolding, and testing of input/output automata over partially ordered I/O streams.
Sep 15 2008, 13:30
Speaker: Linda Postniece
Title: Cutelimination and Proofsearch for BiIntuitionistic Logic Using Nested Sequents
Abstract:
Biintuitionistic logic is the extension of intuitionistic logic with a connective dual to implication. We propose a new sequent calculus for biintuitionistic logic which sits somewhere between display calculi and traditional sequent calculi by using nested sequents. Our calculus enjoys a simple (purely syntactic) cutelimination proof as do display calculi. But it has an easily derivable variant calculus which is amenable to automated proof search as are (some) traditional sequent calculi. As far as we know, our new calculus is the first sequent calculus for biintuitionistic logic which uses no semantic additions like labels, which has a purely syntactic cutelimination proof, and which can be used naturally for backwards proofsearch. (Joint work with Rajeev Gore' and Alwen Tiu)
Sep 15 2008, 14:45
Speaker: Revantha Ramanayake
Title: Valentini's cutelimination for provability logic resolved
Abstract:
In 1983, Valentini presented a syntactic proof of cutelimination for the provability logic GL. The sequent calculus he used was built from sets, as
opposed to multisets, thus avoiding an explicit contraction rule. From a syntactic viewpoint it is more satisfying and formal to explicitly identify applications of the contraction rule. However, it has been claimed recently that Valentini's arguments to eliminate the cutrule do not terminate for sequents built from multisets. This claim has led to much confusion regarding the source of failure. Consequently, various authors have sought new proofs of cutelimination for GL in a multiset setting. In this talk we identify the mistake in the claim and present a proof of cutelimination for sequents built from multisets based on Valentini's original arguments. Complications arising from the contraction rule require special attention. Finally we discuss a generalisation of the cutelimination procedure to tackle two logics that have a similar characteristic axioms, namely Grz and Go.
Jul 24 2008, 15:00
Speaker: Yuxin Deng
Title: Testing Probabilistic Processes
Abstract:
In this talk I will review a natural extension of the testing theory
of De Nicola & Hennessy to processes with probabilistic and
nondeterministic choice. For both the may and must testing preorders,
I present their characterisations in terms of simulations, modal logics,
and inequational axioms in a probabilistic extension of the process
algebra CSP.
(The talk is based on joint work with Rob van Glabbeek, Matthew
Hennessy, Carroll Morgan, and Chenyi Zhang)
Jul 24 2008, 16:00
Speaker: Yuxi Fu
Title: Expressiveness of pi and CCS
Abstract:
Subbisimilarity is proposed as a general tool to classify the
relative expressive power of process calculi. The expressiveness of
several variants of CCS is compared in terms of the subbisimilarity
relationship. Similar investigation is also carried out for the
variants of the pi calculus. The relative expressiveness of the
different forms of the choice operation and the different ways of
introducing infinite behaviors are systematically studied in both
the frameworks of CCS and pi. Some issues concerning the
expressiveness of both CCS and pi are clarified. Several open
problems are solved along the way. The subbisimilarity approach and
the relative expressiveness results can be applied to show the
independence of the operators of the pi calculus. The definition of
the subbisimilarity relationship can be further strengthened with
computational requirement, which leads to a uniform treatment of
computation and interaction.
Jun 13 2008, 14:30
Speaker: Jorge A. Perez
Title: On the Expressiveness and Decidability of HigherOrder Process Calculi
Abstract:
In this talk I will give an overview of a recent work on the
expressiveness of higherorder calculi.
In higherorder process calculi the values exchanged in communications
may contain processes.
I will introduce HOcore, a core calculus of higherorder concurrency;
it has only the operators necessary to express higherorder
communications: input prefix, process output, and parallel composition.
By exhibiting a nearly deterministic encoding of Minsky Machines,
HOcore is shown to be Turing Complete and therefore its termination
problem is undecidable.
Strong bisimilarity, however, is proved to be decidable. Further, the
main forms of strong bisimilarity for higherorder processes
(higherorder bisimilarity, context bisimilarity, normal bisimilarity,
barbed congruence) coincide. They also coincide with their
asynchronous versions.
If time permits, I will discuss two additional results:
(i) a sound and complete axiomatization of bisimilarity, and
(ii) the proof that bisimilarity becomes undecidable if at least four
static (i.e., toplevel) restrictions are added to the calculus.
Jun 17 2008, 14:30
Speaker: Simon Kramer
Title: Reducing Provability to Knowledge in MultiAgent Systems
Abstract:
We construct a reduction of provability to a combination
of four kinds of knowledge in multiagent systems. These
kinds are: individual knowledge (knowledge of messages),
plain propositional knowledge (knowledge that a state of
afairs is the case), common knowledge (propositional
knowledge shared in a community of agents), and a new kind
of knowledge, namely adductive knowledge (propositional
knowledge contingent on the adduction of certain individual
knowledge, e.g., through oracle invocation ).
Keywords: modal logic (conditional, epistemic, provability, and temporal),
knowledge (individual, propositional, common, and adductive),
designatedverifier proofs, multiagent systems
Jun 16 2008, 14:30
Speaker: Roberto Bagnara
Title: On the Design of Generic Static Analyzers for Imperative Languages
Abstract:
The design and implementation of precise static analyzers for
significant fragments of modern imperative languages like C, C++, Java
and Python is a challenging problem. Here we consider a core
imperative language that has several features found in mainstream
languages such as those including recursive functions, runtime system
and userdefined exceptions, and a realistic data and memory
model. For this language we provide a concrete semantics 
characterizing both finite and infinite computations  and a generic
abstract semantics that we prove sound with respect to the concrete
one. We say the abstract semantics is generic since it is designed to
be completely parametric on the analysis domains: in particular, it
provides support for relational domains (i.e., abstract domains that
can capture the relationships between different data objects). We also
sketch how the proposed methodology can be extended to accommodate a
larger language that includes pointers, compound data objects and
nonstructured control flow mechanisms. The approach, which is based
on structured, bigstep operational semantics and on abstract
interpretation, is modular in that the overall static analyzer is
naturally partitioned into components with clearly identified
responsibilities and interfaces, something that greatly simplifies
both the proof of correctness and the implementation.
May 29 2008, 11:00
Speaker: Maribel Fernandez
Title: Nominal Matching and AlphaEquivalence
Abstract:
Nominal matching is matching modulo alphaequality, and has
applications in programming languages and theorem proving, amongst
others. In this talk I will describe efficient algorithms to check the
validity of equations involving binders, and also to solve matching
problems modulo alphaequivalence, using the nominal approach.
May 14 2008, 16:00
Speaker: Simon Kramer
Title: A General Definition of Malware
Abstract:
We propose a general, formal definition of malware in the
language of modal logic. Our definition is general thanks
to its abstract formulation, which, being abstract, is
independent of  but nonetheless generally applicable
to  the manifold concrete manifestations of malware.
From our formulation of malware, we derive equally general
and formal definitions of benware (not malware), antimalware
("antibodies" against malware), and medware ("medecine" for
affected software). We obtain results that express fundamental
relations between malware, benware, antimalware, and medware.
Our general defining principle is causation of (in)correctness.
Keywords:
malware (computer viruses, worms, Trojan horses, etc.), benware,
antimalware, medware, modal logic, formal software engineering
Apr 08 2008, 14:30
Speaker: Carlos Olarte
Title: On the Expressive Power of Universal Timed Concurrent Constraint Programming
Abstract:
The timed concurrent constraint programming model tcc is a process
calculus, closely related to Firstorder lineartemporal logic (FLTL), for modeling
reactive systems. Universal tcc (utcc) is a conservative extension of tcc with an
abstraction operator for modeling mobile reactive systems. It has been shown in the
literature that tcc processes are finitestate and thus cannot encode Turingpowerful
formalisms. In contrast, here we provide encodings in utcc of formalisms
such as Minsky machines and the lambdacalculus. Although both formalisms are Turing
equivalent, these encodings serve different purposes:
The encoding of Minsky machines uses a monadic constraint system which together
with the utcc theory allows us to prove a new undecidability result for a fragment
of FLTL. Namely, the undecidability of the validity problem for monadic FLTL
without equality and function symbols. This result justies the restriction
imposed in previous decidability results on the quantification of flexiblevariables in
monadic FLTL.
The encoding of the lambdacalculus uses instead a polyadic constraint system but it is
compositional unlike that of Minsky machines. Compositionality is an important property
of an encoding as it may allow structural analysis in utcc of the source terms; i.e.,
functional programs.
In summary, we show the full computational expressiveness of utcc,
its compositional correspondence to functional programming (lambdacalculus), and its applicability
for proving new results in standard concurrency formalisms such as FLTL.
Apr 01 2008, 14:30
Speaker: Luca Fossati
Title: A Petri Net Model of Handshake Circuits
Abstract:
We propose a Petri net model of handshake circuits.
Handshake circuits are asynchronous
circuits which enforce several properties such as absence of transmission
interference and insensitivity from delays of propagation on wires. We introduce the notion of handshake Petri net, a Petri net with a
specific external interface. We show that the set of observable
quiescent traces generated by such a net captures the properties
defining a handshake protocol. Conversely we show that for any
handshake protocol we can construct a corresponding net. We
also study different subclasses of the model. Many examples are
provided.
Mar 25 2008, 14:30
Speaker: Jesus Aranda
Title: CCS with Replication in the Chomsky Hierarchy: The Expressive Power of Divergence
Abstract:
A remarkable result in [4] shows that in spite of its being less expressive than CCS w.r.t. weak bisimilarity, CCS! (a CCS variant where infinite behavior is specified by using replication rather than recursion) is Turing powerful. This is done by encoding Random Access Machines (RAM) in CCS!. The encoding is said to be nonfaithful because it may move from a state which can lead to termination into a divergent one which do not correspond to any configuration of the encoded RAM. I.e., the encoding is not termination preserving. In this paper we study the existence of faithful encodings into CCS! of models of computability strictly less expressive than Turing Machines. Namely, grammars of Types 1 (Context Sensitive Languages), 2 (Context Free Languages) and 3 (Regular Languages) in the Chomsky Hierarchy. We provide faithful encodings of Type 3 grammars. We show that it is impossible to provide a faithful encoding of Type 2 grammars and that terminationpreserving CCS! processes can generate languages which are not Type 2. We finally show that the languages generated by terminationpreserving CCS! processes are Type 1 .
[4] N. Busi, M. Gabbrielli, and G. Zavattaro. Comparing recursion, replication, and iteration in process calculi. In ICALP'04, volume 3142
of Lecture Notes in Computer Science, pages 307319. SpringerVerlag, 2004.
Mar 18 2008, 14:30
Speaker: Kazushige Terui
Title: Computational Ludics
Abstract:
We present a computationally adapted version of Girard's ludics, aiming at giving a foundational framework for the computability and complexity theory. We introduce a handy syntax for designs that simplifies and extends Curien's concrete syntax with explicit cuts and identities. We also consider design generators that allow for finite representation of some infinite designs. A normalization procedure in the style of Krivine's abstract machine works on generators directly, giving rise to an effective means of normalization.
Our extended system enjoys the analytical theorems of ludics in a suitably modified form. In addition, we prove a general form of full completeness with respect to coinductively defined behaviours and infinitary proofs.
Finally, an analysis is made on those designs representing data objects. We show that any set of finite data forms a behaviour, and then discuss acceptance of languages via normalization.<>
Mar 13 2008, 10:30
Speaker: Christelle Braun
Title: Overview on Quantum Computation and Quantum Information Theory
Abstract:
Quantum information theory results from the effort in the last decades to generalize classical information theory to the quantum world. This crossdisciplinary study of information processing within quantum mechanics lead to novel achievable limits for the computation and communication capabilities, and demonstrated remarkable effects such as quantum cryptography or teleportation.
After a brief overview on the required basics in quantum mechanics, we will present quantum computation and its relation to the classical approach before giving more insights in quantum information theory and sketching exciting illustrations of this promising field of research.
Feb 28 2008, 14:30
Speaker: Noam Zeilberger
Title: Focusing with higherorder rules
Abstract:
What makes Andreoli's notion of focusing proofs so robust? In this
talk, I will try to argue for the naturality of focusing by giving a
new presentation that makes very explicit the duality between focus
and inversion, and between positive and negative polarity. Loosely
inspired by Girard's ludics, the idea is to stratify the definition of
a focusing sequent calculus into two stages: first define a form of
"patterntyping", and then define the focusing judgments by
quantifying over patterns. Focus quantifies existentially, while
inversion quantifies universallypositive connectives quantify over
constructor patterns, negative connectives over destructor patterns.
Besides giving a simple account of evaluation order and
patternmatching, this style of presentation has the benefit of being
amenable to modular extension, since we potentially can encode many
features into patterntyping without affecting the overall structure
of focusing proofs, or the metaproofs of identity and cut. I will
describe a few of these extensions, which are still preliminary
Feb 22 2008, 14:00
Speaker: Daniele Gorla
Title: Towards a Unified Approach to Encodability and Separation Results
for Process Calculi
Abstract:
In this talk, we present a unified approach to evaluating the relative expressive power of process calculi. In particular, we identify a small set of criteria (that have already been somehow presented in the literature) that an encoding should satisfy to be considered a good means for language comparison. We argue that the combination of such criteria is a valid proposal by noting that:
(i) the best known encodings appeared in the literature satisfy them;
(ii) this notion is not trivial, because there exist encodings that do not satisfy all the criteria we have proposed;
(iii) the best known separation results can be formulated in terms of our criteria; and
(iv) some widely believed (but never proved) separation results can be proved by using the criteria we propose.
Moreover, the way in which we prove known separation results is easier than the way in which such results were originally proved.
Feb 19 2008, 14:00
Speaker: Romain Romain
Title: A probabilistic powerdomain extension for the concurrent constraint
programming
Abstract:
Concurrent constraint programming (CCP, [1]) is a model of computation based
on the notion of store as the information available for the process. Each
process is equiped with a store, with respect to which it tests and adds
constraints. During the execution, the store can only increase, in a
domaintheoreric fashion.
A domaintheoretic denotational semantic has been defined in [2] that maps a
process to the supremum store that it can reach. It is then possible to
compute this supremum store by a fixed point construction, based on the
grammar of the process.
This article studies an extension of concurrent constraint programming with
probabilistic executions. Although similar kinds of extensions have already
been investigated in the literature[3, 4] , we are interested in extending
the original operational and denotational semantics in the most natural way.
To do this, we propose to model the probabilistic CCP as a probabilistic
powerdomain, similar to the one described int [5], built on top of the
original constraint lattice.
We apply those result to a very simple probabilistic CCP based on the original
CCP, with blind probabilistic choice added. Results show a very natural
extension of the original denotational semantic.
References:
[1]: Concurrent Constraint Programming Languages, Vijay A. Saraswat, PhD
Thesis, CarnegieMelon University, 1989
[2]: Semantic Foundations of Concurrent Constraint Programming, Vijay A.
Saraswat and Martin Rinard and Prakash Panangaden, Conference Record of the
Eighteenth Annual {ACM} Symposium on Principles of Programming Languages,
1991
[3]: Probabilistic Concurrent Constraint Programming, Vineet Gupta and Radha
Jagadeesan and Vijay A. Saraswat, International Conference on Concurrency
Theory, 1997
[4]: Stochastic Processes as Concurrent Constraint Programs, Vineet Gupta and
Radha Jagadeesan and Prakash Panangaden, Symposium on Principles of
Programming Languages, 1999
[5]: The troublesome probabilistic powerdomain, A. Jung and R. Tix, Third
Workshop on Computation and Approximation, 1998
Jan 22 2008, 14:00
Speaker: Matteo Capelletti
Title: Parsing with NonAssociative Lambek Grammars
Abstract:
The NonAssociative Lambek calculus (NL, Lambek 1961) is a logic without
structural rules which can be applied to the syntactic and semantic
analysis (of fragments) of natural language. If we look at it as a logical
system, we may want to develop theorem proving methods for its sequents.
While if we look at it as a grammar system, we are interested in
developing parsing systems for its grammars. For NL, the second problem is
more general than the first (since it does not assume any given structure)
and is the one that I will address in my talk. However, the solution that
I propose for parsing with NL grammars also provides (and in fact
presupposes) a solution to the theorem proving problem. Altogether, I will
illustrate a normal form polynomial parsing method for NL grammars.
Jan 15 2008, 14:00
Speaker:
Kosta Dosen
Title: Théorie Générale de la Démonstration
Abstract:
La question centrale de la théorie générale de la
démonstration est la question d'identité des démonstrations 
question traitée ou bien dans le calcul lambda typé ou bien dans la
théorie des catégories. Un aperçu sera donné des résultats obtenus
surtout en traitant la question de cette seconde façon.
