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DVI.
 RS0353

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DVI.
KyungGoo Doh and Peter D. Mosses.
Composing Programming Languages by Combining ActionSemantics
Modules.
December 2003.
39 pp. Appears in Science of Computer Programming, 47(1):236,
2003.
Abstract: This article demonstrates a method for composing a
programming language by combining actionsemantics modules. Each module is
defined separately, and then a programminglanguage module is defined by
combining existing modules. This method enables the language designer to
gradually develop a language by defining, selecting and combining suitable
modules. The resulting modular structure is substantially different from that
previously employed in actionsemantic descriptions.
It also discusses
how to resolve the conflicts that may arise when combining modules, and
indicates some advantages that action semantics has over other approaches in
this respect.
 RS0352

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DVI.
Peter D. Mosses.
Pragmatics of Modular SOS.
December 2003.
22 pp. Invited paper, published in Kirchner and Ringeissen, editors,
Algebraic Methodology and Software Technology: 9th International
Conference, AMAST '02 Proceedings, LNCS 2422, 2002, pages 2140.
Abstract: Modular SOS is a recentlydeveloped variant of
Plotkin's Structural Operational Semantics (SOS) framework. It has several
pragmatic advantages over the original frameworkthe most significant being
that rules specifying the semantics of individual language constructs can be
given definitively, once and for all.
Modular SOS is being used
for teaching operational semantics at the undergraduate level. For this
purpose, the metanotation for modular SOS rules has been made more
userfriendly, and derivation of computations according to the rules is
simulated using Prolog.
After giving an overview of the foundations of
Modular SOS, this paper gives some illustrative examples of the use of the
framework, and discusses various pragmatic aspects.
 RS0351

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DVI.
Ulrich Kohlenbach and Branimir Lambov.
Bounds on Iterations of Asymptotically QuasiNonexpansive
Mappings.
December 2003.
24 pp.
Abstract: This paper establishes explicit quantitative bounds
on the computation of approximate fixed points of asymptotically (quasi)
nonexpansive mappings by means of iterative processes. Here is
a selfmapping of a convex subset of a uniformly convex normed
space . We consider general KrasnoselskiMann iterations with and without
error terms. As a consequence of our quantitative analysis we also get new
qualitative results which show that the assumption on the existence of fixed
points of can be replaced by the existence of approximate fixed points
only. We explain how the existence of effective uniform bounds in this
context can be inferred already apriorily by a logical metatheorem recently
proved by the first author. Our bounds were in fact found with the help of
the general logical machinery behind the proof of this metatheorem. The
proofs we present here are, however, completely selfcontained and do not
require any tools from logic.
 RS0350

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Branimir Lambov.
A TwoLayer Approach to the Computability and Complexity of Real
Numbers.
December 2003.
16 pp.
Abstract: We present a new approach to computability of real
numbers in which real functions have type1 representations, which also
includes the ability to reason about the complexity of real numbers and
functions. We discuss how this allows efficient implementations of exact real
numbers and also present a new real number system that is based on it.
 RS0349

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Marius Mikucionis, Kim G. Larsen, and
Brian Nielsen.
Online OntheFly Testing of Realtime Systems.
December 2003.
14 pp.
Abstract: In this paper we present a framework, an algorithm
and a new tool for online testing of realtime systems based on symbolic
techniques used in UPPAAL model checker. We extend UPPAAL timed automata
network model to a test specification which is used to generate test
primitives and to check the correctness of system responses including the
timing aspects. We use timed trace inclusion as a conformance relation
between system and specification to draw a test verdict. The test generation
and execution algorithm is implemented as an extension to UPPAAL and
experiments carried out to examine the correctness and performance of the
tool. The experiment results are promising.
 RS0348

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Kim G. Larsen, Ulrik Larsen, Brian
Nielsen, Arne Skou, and Andrzej Wasowski.
Danfoss EKC Trial Project Deliverables.
December 2003.
53 pp.
Abstract: This report documents the results of the Danfoss EKC
trial project on model based development using IAR visualState. We present a
formal statemodel of an refrigeration controller based on a specification
given by Danfoss. We report results on modeling, verification, simulation,
and codegeneration. It is found that the IAR visualState is a promising tool
for this application domain, but that improvements must be done to
codegeneration and automatic test generation.
 RS0347

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Hans Hüttel and Jirí Srba.
Recursive PingPong Protocols.
December 2003.
21 pp. To appear in the proceedings of 2004 IFIP WG 1.7, ACM SIGPLAN
and GI FoMSESS Workshop on Issues in the Theory of Security (WITS'04).
Abstract: This paper introduces a process calculus with
recursion which allows us to express an unbounded number of runs of the
pingpong protocols introduced by Dolev and Yao. We study the decidability
issues associated with two common approaches to checking security properties,
namely reachability analysis and bisimulation checking. Our main result is
that our channelfree and memoryless calculus is Turing powerful, assuming
that at least three principals are involved. We also investigate the
expressive power of the calculus in the case of two participants. Here, our
main results are that reachability and, under certain conditions, also strong
bisimilarity become decidable.
 RS0346

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Philipp Gerhardy.
The Role of Quantifier Alternations in Cut Elimination.
December 2003.
10 pp. Extends paper appearing in Baaz and Makowsky, editors, European Association for Computer Science Logic: 17th International
Workshop, CSL '03 Proceedings, LNCS 2803, 2003, pages 212225.
Abstract: Extending previous results from the author's master's
thesis, subsequently published in the proceedings of CSL 2003, on the
complexity of cut elimination for the sequent calculus LK, we discuss
the role of quantifier alternations and develope a measure to describe the
complexity of cut elimination in terms of quantifier alternations in cut
formulas and contractions on such formulas.
 RS0345

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DVI.
Peter Bro Miltersen, Jaikumar
Radhakrishnan, and Ingo Wegener.
On converting CNF to DNF.
December 2003.
11 pp. A preliminary version appeared in Rovan and Vojtás,
editors, Mathematical Foundations of Computer Science: 28th
International Symposium, MFCS '03 Proceedings, LNCS 2747, 2003, pages
612621.
Abstract: We study how big the blowup in size can be when one
switches between the CNF and DNF representations of boolean functions. For a
function
,
denotes
the minimum number of clauses in a CNF for ; similarly,
denotes the minimum number of terms in a DNF for . For
, let
be the maximum
for a function
with
. We show that there are constants
and
, such that for all large and all
, we have
In particular, when is the polynomial , we get
.
 RS0344

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Anna Gál and Peter Bro Miltersen.
The Cell Probe Complexity of Succinct Data Structures.
December 2003.
17 pp. Appears in Lingas and Nilsson, editors, Fundamentals of
Computation Theory: 14th International Conference, FCT '03 Proceedings,
LNCS 2751, 2003, pages 442453. An early version of this paper appeared in
Baeten, Lenstra, Parrow and Woeginger, editors, 30th International
Colloquium on Automata, Languages, and Programming, ICALP '03 Proceedings,
LNCS 2719, 2003, pages 332344.
Abstract: In the cell probe model with word size 1 (the bit
probe model), a static data structure problem is given by a map
, where is a set of possible
data to be stored, is a set of possible queries (for natural
problems, we have ) and is the answer to question about
data .
A solution is given by a representation
and a query algorithm so that
. The time of the query algorithm is the number of bits it reads
in .
In this paper, we consider the case of succinct
representations where for some redundancy . For a
boolean version of the problem of polynomial evaluation with preprocessing of
coefficients, we show a lower bound on the redundancyquery time tradeoff of
the form
In particular, for very small
redundancies , we get an almost optimal lower bound stating that the query
algorithm has to inspect almost the entire data structure (up to a
logarithmic factor). We show similar lower bounds for problems satisfying a
certain combinatorial property of a coding theoretic flavor. Previously, no
lower bounds were known on in the general model for explicit
functions, even for very small redundancies.
By restricting our
attention to systematic or index structures satisfying
for some map (where denotes
concatenation) we show similar lower bounds on the redundancyquery time
tradeoff for the natural data structuring problems of Prefix Sum and
Substring Search.
 RS0343

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Mikkel Nygaard and Glynn Winskel.
Domain Theory for Concurrency.
December 2003.
45 pp. To appear in a Theoretical Computer Science special
issue on Domain Theory.
Abstract: A simple domain theory for concurrency is presented.
Based on a categorical model of linear logic and associated comonads, it
highlights the role of linearity in concurrent computation. Two choices of
comonad yield two expressive metalanguages for higherorder processes, both
arising from canonical constructions in the model. Their denotational
semantics are fully abstract with respect to contextual equivalence. One
language derives from an exponential of linear logic; it supports a
straightforward operational semantics with simple proofs of soundness and
adequacy. The other choice of comonad yields a model of affinelinear logic,
and a process language with a tensor operation to be understood as a parallel
composition of independent processes. The domain theory can be generalised to
presheaf models, providing a more refined treatment of nondeterministic
branching. The article concludes with a discussion of a broader programme of
research, towards a fully fledged domain theory for concurrency.
 RS0342

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Mikkel Nygaard and Glynn Winskel.
Full Abstraction for HOPLA.
December 2003.
25 pp. Appears in Amadio and Lugiez, editors, Concurrency
Theory: 14th International Conference, CONCUR '03 Proceedings, LNCS 2761,
2003, pages 383398.
Abstract: A fully abstract denotational semantics for the
higherorder process language HOPLA is presented. It characterises contextual
and logical equivalence, the latter linking up with simulation. The semantics
is a clean, domaintheoretic description of processes as downwardsclosed
sets of computation paths: the operations of HOPLA arise as syntactic
encodings of canonical constructions on such sets; full abstraction is a
direct consequence of expressiveness with respect to computation paths; and
simple proofs of soundness and adequacy shows correspondence between the
denotational and operational semantics.
 RS0341

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Malgorzata Biernacka, Dariusz Biernacki,
and Olivier Danvy.
An Operational Foundation for Delimited Continuations.
December 2003.
21 pp.
Abstract: We derive an abstract machine that corresponds to a
definitional interpreter for the control operators shift and reset. Based on
this abstract machine, we construct a syntactic theory of delimited
continuations.
Both the derivation and the construction scale to the
family of control operators shift and reset. The definitional
interpreter for shift and reset has layers of continuations,
the corresponding abstract machine has layers of control stacks, and
the corresponding syntactic theory has layers of evaluation contexts.
 RS0340

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Andrzej Filinski and Henning Korsholm
Rohde.
A Denotational Account of Untyped Normalization by Evaluation.
December 2003.
29 pp.
Abstract: We show that the standard normalizationbyevaluation
construction for the simplytyped
calculus has a
natural counterpart for the untyped calculus, with the
central typeindexed logical relation replaced by a ``recursively defined''
invariant relation, in the style of Pitts. In fact, the construction
can be seen as generalizing a computationaladequacy argument for an untyped,
callbyname language to normalization instead of evaluation.
In the
untyped setting, not all terms have normal forms, so the normalization
function is necessarily partial. We establish its correctness in the senses
of soundness (the output term, if any, is equivalent to the
input term); standardization (equivalent terms are mapped to
the same result); and completeness (the function is defined for all
terms that do have normal forms). We also show how the semantic construction
enables a simple yet formal correctness proof for the normalization
algorithm, expressed as a functional program in an MLlike callbyvalue
language.
 RS0339

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Jörg Abendroth.
Applying Calculus to Practice: An Example of a Unified
Security Mechanism.
November 2003.
35 pp.
Abstract: The Picalculus has been developed to reason about
behavioural equivalence. Different notions of equivalence are defined in
terms of process interactions, as well as the context of processes. There are
various extensions of the Picalculus, such as the SPI calculus, which has
primitives to facilitate security protocol design.
Another area of
computer security is access control research, which includes problems of
access control models, policies and access control mechanism. The design of a
unified framework for access control requires that all policies are supported
and different access control models are instantiated correctly.
In
this paper we will utilise the Pi calculus to reason about access control
policies and mechanism. An equivalence of different policy implementations,
as well as access control mechanism will be shown. Finally some experiences
regarding the use of Picalculus are presented.
 RS0338

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Henning Böttger, Anders Møller, and
Michael I. Schwartzbach.
Contracts for Cooperation between Web Service Programmers and
HTML Designers.
November 2003.
23 pp.
Abstract: Interactive Web services consist of a mixture of HTML
fragments and program code. The fragments, which are maintained by designers,
are combined to form HTML pages that are shown to the clients. The code,
which is maintained by programmers, is executed on the server to handle the
business logic. Current Web service frameworks provide little help in
separating these constituents, which complicates cooperation between
programmers and HTML designers.
We propose a system based on XML
templates and formalized contracts allowing a flexible separation of
concerns. The contracts act as interfaces between the programmers and the
HTML designers and permit tool support for statically checking that both
parties fulfill their obligations. This ensures that (1) programmers and HTML
designers work more independently focusing on their own expertises, (2) the
Web service implementation is better structured and thus easier to develop
and maintain, (3) it is guaranteed that only valid HTML is sent to the
clients even though it is constructed dynamically, (4) the programmer uses
the XML templates consistently, and (5) the form input fields being sent to
the client always match the code receiving those values. Additionally, we
describe tools that aid in the construction and management of contracts and
XML templates.
 RS0337

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Claude Crépeau, Paul Dumais, Dominic
Mayers, and Louis Salvail.
Computational Collapse of Quantum State with Application to
Oblivious Transfer.
November 2003.
30 pp.
Abstract: Quantum 2party cryptography differs from its
classical counterpart in at least one important way: Given blakbox access to
a perfect commitment scheme there exists a secure quantum
oblivious transfer. This reduction proposed by Crépeau and Kilian was
proved secure against any receiver by Yao, in the case where perfect
commitments are used. However, quantum commitments would normally be based on
computational assumptions. A natural question therefore arises: What happens
to the security of the above reduction when computationally secure
commitments are used instead of perfect ones?
In this paper, we
address the security of QOT when computationally binding string
commitments are available. In particular, we analyse the security of a
primitive called Quantum Measurement Commitment when it is constructed
from unconditionally concealing but computationally binding commitments. As
measuring a quantum state induces an irreversible collapse, we describe a QMC
as an instance of ``computational collapse of a quantum state''. In a QMC a
state appears to be collapsed to a polynomial time observer who cannot
extract full information about the state without breaking a computational
assumption.
We reduce the security of QMC to a weak binding
criteria for the string commitment. We also show that secure QMCs
implies QOT using a straightforward variant of the reduction above.
 RS0336

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Ivan B. Damgård, Serge Fehr, Kirill
Morozov, and Louis Salvail.
Unfair Noisy Channels and Oblivious Transfer.
November 2003.
26 pp. Appears in Naor, editor, The first Theory of Cryptography
Conference, TCC '04 Proceedings, LNCS 2951, 2004, pages 355373.
Abstract: In a paper from EuroCrypt'99, Damgård, Kilian and
Salvail show various positive and negative results on constructing Bit
Commitment (BC) and Oblivious Transfer (OT) from Unfair Noisy Channels (UNC),
i.e., binary symmetric channels where the error rate is only known to be in a
certain interval
and can be chosen adversarily. They also
introduce a related primitive called . We prove in this paper
that any OT protocol that can be constructed based on a and is
secure against a passive adversary can be transformed using a generic
``compiler'' into an OT protocol based on a which is secure against an
active adversary. Apart from making positive results easier to prove in
general, this also allows correcting a problem in the EuroCrypt'99 paper:
There, a positive result was claimed on constructing from UNC an OT that is
secure against active cheating. We point out that the proof sketch given for
this was incomplete, and we show that a correct proof of a much stronger
result follows from our general compilation result and a new technique for
transforming between weaker versions of OT with different parameters.
 RS0335

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Mads Sig Ager, Olivier Danvy, and Jan
Midtgaard.
A Functional Correspondence between Monadic Evaluators and
Abstract Machines for Languages with Computational Effects.
November 2003.
31 pp.
Abstract: We extend our correspondence between evaluators and
abstract machines from the pure setting of the lambdacalculus to the impure
setting of the computational lambdacalculus. Specifically, we show how to
derive new abstract machines from monadic evaluators for the computational
lambdacalculus. Starting from a monadic evaluator and a given monad, we
inline the components of the monad in the evaluator and we derive the
corresponding abstract machine by closureconverting, CPStransforming, and
defunctionalizing this inlined interpreter. We illustrate the construction
first with the identity monad, obtaining yet again the CEK machine, and then
with a state monad, an exception monad, and a combination of both.
In
addition, we characterize the tailrecursive stack inspection presented by
Clements and Felleisen at ESOP 2003 as a canonical state monad. Combining
this state monad with an exception monad, we construct an abstract machine
for a language with exceptions and properly tailrecursive stack inspection.
The construction scales to other monadsincluding one more properly
dedicated to stack inspection than the state monadand other monadic
evaluators.
 RS0334

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Luca Aceto, Willem Jan Fokkink, Anna
Ingólfsdóttir, and Bas Luttik.
CCS with Hennessy's Merge has no Finite Equational
Axiomatization.
November 2003.
37 pp.
Abstract: This paper confirms a conjecture of Bergstra and
Klop's from 1984 by establishing that the process algebra obtained by adding
an auxiliary operator proposed by Hennessy in 1981 to the recursion free
fragment of Milner's Calculus of Communicationg Systems is not finitely based
modulo bisimulation equivalence. Thus Hennessy's merge cannot replace the
left merge and communication merge operators proposed by Bergstra and Klop,
at least if a finite axiomatization of parallel composition is desired.
 RS0333

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Olivier Danvy.
A Rational Deconstruction of Landin's SECD Machine.
October 2003.
32 pp. This report supersedes the earlier BRICS report RS0253.
Abstract: Landin's SECD machine was the first abstract machine
for the calculus viewed as a programming language. Both
theoretically as a model of computation and practically as an idealized
implementation, it has set the tone for the subsequent development of
abstract machines for functional programming languages. However, and even
though variants of the SECD machine have been presented, derived, and
invented, the precise rationale for its architecture and modus operandi has
remained elusive. In this article, we deconstruct the SECD machine into a
interpreter, i.e., an evaluation function, and we reconstruct
interpreters into a variety of SECDlike machines. The
deconstruction and reconstructions are transformational: they are based on
equational reasoning and on a combination of simple program
transformationsmainly closure conversion, transformation into
continuationpassing style, and defunctionalization.
The evaluation
function underlying the SECD machine provides a precise rationale for its
architecture: it is an environmentbased evalapply evaluator with a
calleesave strategy for the environment, a data stack of intermediate
results, and a control delimiter. Each of the components of the SECD machine
(stack, environment, control, and dump) is therefore rationalized and so are
its transitions.
The deconstruction and reconstruction method also
applies to other abstract machines and other evaluation functions. It makes
it possible to systematically extract the denotational content of an abstract
machine in the form of a compositional evaluation function, and the
(smallstep) operational content of an evaluation function in the form of an
abstract machine.
 RS0332

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Philipp Gerhardy and Ulrich Kohlenbach.
Extracting Herbrand Disjunctions by Functional
Interpretation.
October 2003.
17 pp.
Abstract: Carrying out a suggestion by Kreisel, we adapt
Gödel's functional interpretation to ordinary firstorder predicate
logic(PL) and thus devise an algorithm to extract Herbrand terms from
PLproofs. The extraction is carried out in an extension of PL to higher
types. The algorithm consists of two main steps: first we extract a
functional realizer, next we compute the normalform of the realizer
from which the Herbrand terms can be read off. Even though the extraction is
carried out in the extended language, the terms are ordinary PLterms. In
contrast to approaches to Herbrand's theorem based on cut elimination or
elimination this extraction technique is, except for the
normalization step, of low polynomial complexity, fully modular and
furthermore allows an analysis of the structure of the Herbrand terms, in the
spirit of Kreisel, already prior to the normalization step. It is expected
that the implementation of functional interpretation in Schwichtenberg's
MINLOG system can be adapted to yield an efficient Herbrandterm extraction
tool.
 RS0331

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Stephen Lack and Pawe Sobocinski.
Adhesive Categories.
October 2003.
25 pp.
Abstract: We introduce adhesive categories, which are
categories with structure ensuring that pushouts along monomorphisms are
wellbehaved. Many types of graphical structures used in computer science are
shown to be examples of adhesive categories. Doublepushout graph rewriting
generalises well to rewriting on arbitrary adhesive categories.
 RS0330

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Jesper Makholm Byskov,
Bolette Ammitzbøll Madsen, and Bjarke Skjernaa.
New Algorithms for Exact Satisfiability.
October 2003.
31 pp.
Abstract: The Exact Satisfiability problem is to determine if a
CNFformula has a truth assignment satisfying exactly one literal in each
clause; Exact 3Satisfiability is the version in which each clause contains
at most three literals. In this paper, we present algorithms for Exact
Satisfiability and Exact 3Satisfiability running in time
and
, respectively. The previously best algorithms have
running times
for Exact Satisfiability (Monien, Speckenmeyer
and Vornberger (1981)) and
for Exact 3Satisfiability
(Kulikov and independently Porschen, Randerath and Speckenmeyer (2002)). We
extend the case analyses of these papers and observe, that a formula not
satisfying any of our cases has a small number of variables, for which we can
try all possible truth assignments and for each such assignment solve the
remaining part of the formula in polynomial time.
 RS0329

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Aske Simon Christensen, Christian
Kirkegaard, and Anders Møller.
A Runtime System for XML Transformations in Java.
October 2003.
15 pp.
Abstract: We show that it is possible to extend a
generalpurpose programming language with a convenient highlevel datatype
for manipulating XML documents while permitting (1) precise static analysis
for guaranteeing validity of the constructed XML documents relative to the
given DTD schemas, and (2) a runtime system where the operations can be
performed efficiently. The system, named XACT, is based on a notion of
immutable XML templates and uses XPath for deconstructing documents. A
companion paper presents the program analysis; this paper focuses on the
efficient runtime representation.
 RS0328

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DVI.
Zoltán Ésik and Kim G. Larsen.
Regular Languages Definable by Lindström Quantifiers.
August 2003.
82 pp. This report supersedes the earlier BRICS report RS0220.
Abstract: In our main result, we establish a formal connection
between Lindström quantifiers with respect to regular languages and the
double semidirect product of finite monoids with a distinguished set of
generators. We use this correspondence to characterize the expressive power
of Lindström quantifiers associated with a class of regular languages.
 RS0327

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DVI.
Luca Aceto, Willem Jan Fokkink, Rob J. van
Glabbeek, and Anna Ingólfsdóttir.
Nested Semantics over Finite Trees are Equationally Hard.
August 2003.
31 pp.
Abstract: This paper studies nested simulation and nested trace
semantics over the language BCCSP, a basic formalism to express finite
process behaviour. It is shown that none of these semantics affords finite
(in)equational axiomatizations over BCCSP. In particular, for each of the
nested semantics studied in this paper, the collection of sound, closed
(in)equations over a singleton action set is not finitely based.
 RS0326

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DVI.
Olivier Danvy and Ulrik P. Schultz.
LambdaLifting in Quadratic Time.
August 2003.
23 pp. Extended version of a paper appearing in Hu and
RodríguezArtalejo, editors, Sixth International Symposium on
Functional and Logic Programming, FLOPS '02 Proceedings, LNCS 2441, 2002,
pages 134151. This report supersedes the earlier BRICS report RS0230.
Abstract: Lambdalifting is a program transformation used in
compilers and in partial evaluators and that operates in cubic time. In this
article, we show how to reduce this complexity to quadratic time, and we
present a flowsensitive lambdalifter that also works in quadratic
time.
Lambdalifting transforms a blockstructured program into a set
of recursive equations, one for each local function in the source program.
Each equation carries extra parameters to account for the free variables of
the corresponding local function and of all its callees. It is the
search for these extra parameters that yields the cubic factor in the
traditional formulation of lambdalifting, which is due to Johnsson. This
search is carried out by a transitive closure.
Instead, we partition
the call graph of the source program into strongly connected components,
based on the simple observation that all functions in each component
need the same extra parameters and thus a transitive closure is not needed.
We therefore simplify the search for extra parameters by treating each
strongly connected component instead of each function as a unit, thereby
reducing the time complexity of lambdalifting from
to
, where is the size of the program.
Since a
lambdalifter can output programs of size , we believe that
our algorithm is close to optimal.
 RS0325

Biernacki Dariusz and Danvy Olivier.
From Interpreter to Logic Engine by Defunctionalization.
June 2003.
13 pp. Presented at the International Symposium on Logic Based
Program Development and Transformation, LOPSTR 2003, Uppsala, Sweden, August
2527, 2003. This report is superseded by the later report
BRICS RS045.
Abstract: Starting from a continuationbased interpreter for a
simple logic programming language, propositional Prolog with cut, we derive
the corresponding logic engine in the form of an abstract machine. The
derivation originates in previous work (our article at PPDP 2003) where it
was applied to the lambdacalculus. The key transformation here is Reynolds's
defunctionalization that transforms a tailrecursive, continuationpassing
interpreter into a transition system, i.e., an abstract machine. Similar
denotational and operational semantics were studied by de Bruin and de Vink
in previous work (their article at TAPSOFT 1989), and we compare their study
with our derivation. Additionally, we present a directstyle interpreter of
propositional Prolog expressed with control operators for delimited
continuations.
 RS0324

Mads Sig Ager, Olivier Danvy, and Jan Midtgaard.
A Functional Correspondence between CallbyNeed Evaluators and
Lazy Abstract Machines.
June 2003.
13 pp. This report is superseded by the later report
BRICS RS043.
Abstract: We bridge the gap between compositional evaluators
and abstract machines for the lambdacalculus, using closure conversion,
transformation into continuationpassing style, and defunctionalization of
continuations. This article is a spinoff of our article at PPDP 2003, where
we consider call by name and call by value. Here, however, we consider call
by need.
We derive a lazy abstract machine from an ordinary
callbyneed evaluator that threads a heap of updatable cells. In this
resulting abstract machine, the continuation fragment for updating a heap
cell naturally appears as an `update marker', an implementation technique
that was invented for the Three Instruction Machine and subsequently used to
construct lazy variants of Krivine's abstract machine. Tuning the evaluator
leads to other implementation techniques such as unboxed values and the
pushenter model. The correctness of the resulting abstract machines is a
corollary of the correctness of the original evaluators and of the program
transformations used in the derivation.
 RS0323

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DVI.
Margarita Korovina.
Recent Advances in definability over Continuous Data
Types.
June 2003.
24 pp.
Abstract: The purpose of this paper is to survey our recent
research in computability and definability over continuous data types such as
the real numbers, realvalued functions and functionals. We investigate the
expressive power and algorithmic properties of the language of
formulas intended to represent computability over the real numbers.
In order to adequately represent computability we extend the reals by the
structure of hereditarily finite sets. In this setting it is crucial to
consider the real numbers without equality since the equality test is
undecidable over the reals. We prove Engeler's Lemma for
definability over the reals without the equality test which relates
definability with definability in the constructive infinitary
language
. Thus, a relation over the real numbers is
definable if and only if it is definable by a disjunction of a
recursively enumerable set of quantifier free formulas. This result reveals
computational aspects of definability and also gives topological
characterisation of definable relations over the reals without the
equality test. We also illustrate how computability over the real numbers can
be expressed in the language of formulas.
 RS0322

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PDF,
DVI.
Ivan B. Damgård and Mads J. Jurik.
Scalable KeyEscrow.
May 2003.
15 pp.
Abstract: We propose a cryptosystem that has an inherent key
escrow mechanism. This leads us to propose a session based public verifiable
key escrow system that greatly improves the amount of key material the escrow
servers has to keep in order to decrypt an encryption. In our scheme the
servers will only have a single secret sharing, as opposed to a single key
from every escrowed player. This is done while still having the properties:
1) public verifiable: the user proves to everyone that the encryption can
indeed be escrowed, and 2) no secret leakage: no matter how many decryptions
a law enforcement agency is presented, it will gain no more information on
the users private key, than it couldn't have calculated itself.
 RS0321

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PDF,
DVI.
Ulrich Kohlenbach.
Some Logical Metatheorems with Applications in Functional
Analysis.
May 2003.
55 pp. Slighly revised and extended version to appear in Transactions of the American Mathematical Society.
Abstract: In previous papers we have developed prooftheoretic
techniques for extracting effective uniform bounds from large classes of
ineffective existence proofs in functional analysis. `Uniform' here means
independence from parameters in compact spaces. A recent case study in fixed
point theory systematically yielded uniformity even w.r.t. parameters in
metrically bounded (but noncompact) subsets which had been known before only
in special cases. In the present paper we prove general logical metatheorems
which cover these applications to fixed point theory as special cases but are
not restricted to this area at all. Our theorems guarantee under general
logical conditions such strong uniform versions of nonuniform existence
statements. Moreover, they provide algorithms for actually extracting
effective uniform bounds and transforming the original proof into one for the
stronger uniformity result. Our metatheorems deal with general classes of
spaces like metric spaces, hyperbolic spaces, normed linear spaces, uniformly
convex spaces as well as inner product spaces.
 RS0320

PostScript,
PDF.
Mads Sig Ager, Olivier Danvy, and
Henning Korsholm Rohde.
Fast Partial Evaluation of Pattern Matching in Strings.
May 2003.
16 pp. Final version in Leuschel, editor, ACM SIGPLAN Workshop
on Partial Evaluation and SemanticsBased Program Manipulation, PEPM '03
Proceedings, 2003, pages 39. This report supersedes the earlier BRICS
report RS0311.
Abstract: We show how to obtain all of Knuth, Morris, and
Pratt's lineartime string matcher by partial evaluation of a quadratictime
string matcher with respect to a pattern string. Although it has been known
for 15 years how to obtain this linear matcher by partial evaluation of a
quadratic one, how to obtain it in linear time has remained an open
problem.
Obtaining a linear matcher by partial evaluation of a
quadratic one is achieved by performing its backtracking at specialization
time and memoizing its results. We show (1) how to rewrite the source matcher
such that its static intermediate computations can be shared at
specialization time and (2) how to extend the memoization capabilities of a
partial evaluator to static functions. Such an extended partial evaluator, if
its memoization is implemented efficiently, specializes the rewritten source
matcher in linear time.
 RS0319

PostScript,
PDF.
Christian Kirkegaard, Anders Møller,
and Michael I. Schwartzbach.
Static Analysis of XML Transformations in Java.
May 2003.
29 pp.
Abstract: XML documents generated dynamically by programs are
typically represented as text strings or DOM trees. This is a lowlevel
approach for several reasons: 1) Traversing and modifying such structures can
be tedious and error prone; 2) Although schema languages, e.g. DTD, allow
classes of XML documents to be defined, there are generally no automatic
mechanisms for statically checking that a program transforms from one class
to another as intended. We introduce XACT, a highlevel approach for
Java using XML templates as a firstclass data type with operations for
manipulating XML values based on XPath. In addition to an efficient runtime
representation, the data type permits static type checking using DTD schemas
as types. By specifying schemas for the input and output of a program, our
algorithm will statically verify that valid input data is always transformed
into valid output data and that no errors occur during processing.
 RS0318

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PDF,
DVI.
Bartek Klin and Pawe Sobocinski.
Syntactic Formats for Free: An Abstract Approach to Process
Equivalence.
April 2003.
41 pp. Appears in Amadio and Lugiez, editors, Concurrency
Theory: 14th International Conference, CONCUR '03 Proceedings, LNCS 2761,
2003, pages 7286.
Abstract: A framework of Plotkin and Turis, originally aimed at
providing an abstract notion of bisimulation, is modified to cover other
operational equivalences and preorders. Combined with bialgebraic methods, it
yields a technique for deriving syntactic formats for transition system
specifications, which guarantee operational preorders to be precongruences.
The technique is applied to the trace prorder, the completed trace preorder
and the failures preorder. In the latter two cases, new syntactic formats
guaranteeing precongruence properties are introduced.
 RS0317

PostScript,
PDF.
Luca Aceto, Jens Alsted Hansen, Anna
Ingólfsdóttir, Jacob Johnsen, and John Knudsen.
The Complexity of Checking Consistency of Pedigree Information
and Related Problems.
March 2003.
31 pp. This paper supersedes BRICS Report RS0242.
Abstract: Consistency checking is a fundamental computational
problem in genetics. Given a pedigree and information on the genotypes (of
some) of the individuals in it, the aim of consistency checking is to
determine whether these data are consistent with the classic Mendelian laws
of inheritance. This problem arose originally from the geneticists' need to
filter their input data from erroneous information, and is well motivated
from both a biological and a sociological viewpoint. This paper shows that
consistency checking is NPcomplete, even with focus on a single gene and in
the presence of three alleles. Several other results on the computational
complexity of problems from genetics that are related to consistency checking
are also offered. In particular, it is shown that checking the consistency of
pedigrees over two alleles, and of pedigrees without loops, can be done in
polynomial time.
 RS0316

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PDF,
DVI.
Ivan B. Damgård and Mads J. Jurik.
A LengthFlexible Threshold Cryptosystem with Applications.
March 2003.
31 pp.
Abstract: We propose a publickey cryptosystem which is derived
from the Paillier cryptosystem. The scheme inherits the attractive
homomorphic properties of Paillier encryption. In addition, we achieve two
new properties: First, all users can use the same modulus when generating key
pairs, this allows more efficient proofs of relations between different
encryptions. Second, we can construct a threshold decryption protocol for our
scheme that is length flexible, i.e., it can handle efficiently messages of
arbitrary length, even though the public key and the secret key shares held
by decryption servers are of fixed size. We show how to apply this
cryptosystem to build:
1) a selftallying election scheme with perfect
ballot secrecy. This is a small voting system where the result can be
computed from the submitted votes without the need for decryption servers.
The votes are kept secret unless the cryptosystem can be broken, regardless
of the number of cheating parties. This is in contrast to other known schemes
that usually require a number of decryption servers, the majority of which
must be honest.
2) a lengthflexible mixnet which is universally
verifiable, where the size of keys and ciphertexts do not depend on the
number of mix servers, and is robust against a corrupt minority. Mixnets can
provide anonymity by shuffling messages to provide a random permutation of
input ciphertexts to the output plaintexts such that no one knows which
plaintexts relate to which ciphertexts. The mixnet inherits several nice
properties from the underlying cryptosystem, thus making it useful for a
setting with small messages or high computational power, lowband width and
that anyone can verify that the mix have been done correctly.
 RS0315

PostScript,
PDF,
DVI.
Anna Ingólfsdóttir.
A Semantic Theory for ValuePassing Processes Based on the Late
Approach.
March 2003.
48 pp.
Abstract: A general class of languages for valuepassing
calculi based on the late semantic approach is defined and a concrete
instantiation of the general syntax is given. This is a modification of the
standard according to the late approach. Three kinds of semantics are
given for this language. First a Plotkin style operational semantics by means
of an applicative labelled transition system is introduced. This is a
modification of the standard labelled transition system that caters for
valuepassing according to the late approach. As an abstraction, late
bisimulation preorder is given. Then a general class of denotational models
for the late semantics is defined. A denotational model for the concrete
language is given as an instantiation of the general class. Two equationally
based proof systems are defined. The first one, which is valuefinitary,
i. e. only reasons about a finite number of values at each time, is shown to
be sound and complete with respect to this model. The second proof system, a
valueinfinitary one, is shown to be sound with respect to the model, whereas
the completeness is proven later. The operational and the denotational
semantics are compared and it is shown that the bisimulation preorder is
finer than the preorder induced by the denotational model. We also show that
in general the bisimulation preorder is strictly included in the
model induced preorder. Finally a valuefinitary version of the bisimulation
preorder is defined and the full abstractness of the denotational model with
respect to it is shown. It is also shown that for the
bisimulation preorder coincides with the preorder induced by the
model. From this we can conclude that if we allow for parameterized recursion
in our language, we may express processes which coincide in any algebraic
domain but are distinguished by the bisimulation. This shows that
if we extend in this way we obtain a strictly more expressive
language.
 RS0314

PostScript,
PDF,
DVI.
Mads Sig Ager, Dariusz Biernacki, Olivier
Danvy, and Jan Midtgaard.
From Interpreter to Compiler and Virtual Machine: A Functional
Derivation.
March 2003.
36 pp.
Abstract: We show how to derive a compiler and a virtual
machine from a compositional interpreter. We first illustrate the derivation
with two evaluation functions and two normalization functions. We obtain
Krivine's machine, Felleisen et al.'s CEK machine, and a generalization of
these machines performing strong normalization, which is new. We observe that
several existing compilers and virtual machinese.g., the Categorical
Abstract Machine (CAM), Schmidt's VEC machine, and Leroy's Zinc abstract
machineare already in derived form and we present the corresponding
interpreter for the CAM and the VEC machine. We also consider Hannan and
Miller's CLS machine and Landin's SECD machine.
We derived Krivine's
machine via a callbyname CPS transformation and the CEK machine via a
callbyvalue CPS transformation. These two derivations hold both for an
evaluation function and for a normalization function. They provide a
nontrivial illustration of Reynolds's warning about the evaluation order of
a metalanguage.
 RS0313

PostScript,
PDF,
DVI.
Mads Sig Ager, Dariusz Biernacki, Olivier
Danvy, and Jan Midtgaard.
A Functional Correspondence between Evaluators and Abstract
Machines.
March 2003.
28 pp.
Abstract: We bridge the gap between functional evaluators and
abstract machines for the lambdacalculus, using closure conversion,
transformation into continuationpassing style, and defunctionalization of
continuations.
We illustrate this bridge by deriving Krivine's
abstract machine from an ordinary callbyname evaluator and by deriving an
ordinary callbyvalue evaluator from Felleisen et al.'s CEK machine. The
first derivation is strikingly simpler than what can be found in the
literature. The second one is new. Together, they show that Krivine's
abstract machine and the CEK machine correspond to the callbyname and
callbyvalue facets of an ordinary evaluator for the lambdacalculus.
We then reveal the denotational content of Hannan and Miller's CLS machine
and of Landin's SECD machine. We formally compare the corresponding
evaluators and we illustrate some relative degrees of freedom in the design
spaces of evaluators and of abstract machines for the lambdacalculus with
computational effects.
For the purpose of this work, we distinguish
between virtual machines, which have an instruction set, and abstract
machines, which do not. The Categorical Abstract Machine, for example, has an
instruction set, but Krivine's machine, the CEK machine, the CLS machine, and
the SECD machine do not; they directly operate on lambdaterms instead. We
present the abstract machine that corresponds to the Categorical Abstract
Machine.
 RS0312

PostScript,
PDF,
DVI.
MirceaDan Hernest and Ulrich Kohlenbach.
A Complexity Analysis of Functional Interpretations.
February 2003.
70 pp.
Abstract: We give a quantitative analysis of Gödel's
functional interpretation and its monotone variant. The two have been used
for the extraction of programs and numerical bounds as well as for
conservation results. They apply both to (semi)intuitionistic as well as
(combined with negative translation) classical proofs. The proofs may be
formalized in systems ranging from weak base systems to arithmetic and
analysis (and numerous fragments of these). We give upper bounds in basic
proof data on the depth, size, maximal type degree and maximal type arity of
the extracted terms as well as on the depth of the verifying proof. In all
cases terms of size linear in the size of the proof at input can be extracted
and the corresponding extraction algorithms have cubic worsttime complexity.
The verifying proofs have depth linear in the depth of the proof at input and
the maximal size of a formula of this proof.
 RS0311

Mads Sig Ager, Olivier Danvy, and Henning Korsholm Rohde.
Fast Partial Evaluation of Pattern Matching in Strings.
February 2003.
14 pp. This report is superseded by the later report
BRICS RS0320.
Abstract: We show how to obtain all of Knuth, Morris, and
Pratt's lineartime string matcher by partial evaluation of a quadratictime
string matcher with respect to a pattern string. Although it has been known
for 15 years how to obtain this linear matcher by partial evaluation of a
quadratic one, how to obtain it in linear time has remained an open
problem.
Obtaining a linear matcher by partial evaluation of a
quadratic one is achieved by performing its backtracking at specialization
time and memoizing its results. We show (1) how to rewrite the source matcher
such that its static intermediate computations can be shared at
specialization time and (2) how to extend the memoization capabilities of a
partial evaluator to static functions. Such an extended partial evaluator, if
its memoization is implemented efficiently, specializes the rewritten source
matcher in linear time.
 RS0310

PostScript,
PDF.
Federico Crazzolara and Giuseppe Milicia.
Wireless Authentication in Spaces.
February 2003.
20 pp.
Abstract: The Spaces framework provides a set of tools
to support every step of the security protocol's lifecycle. The framework
includes a simple, yet powerful programming language which is an
implementation of the Security Protocol Language (SPL). SPL is a formal
calculus designed to model security protocols and prove interesting
properties about them. In this paper we take an authentication protocol
suited for lowpower wireless devices and derive a Spaces
implementation from its SPL model. We study the correctness of the resulting
implementation using the underlying SPL semantics of Spaces.
 RS039

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PDF.
Ivan B. Damgård and Gudmund Skovbjerg
Frandsen.
An Extended Quadratic Frobenius Primality Test with Average
and Worst Case Error Estimates.
February 2003.
53 pp. Appears in Lingas and Nilsson, editors, Fundamentals of
Computation Theory: 14th International Conference, FCT '03 Proceedings,
LNCS 2751, 2003, pages 118131.
Abstract: We present an Extended Quadratic Frobenius Primality
Test (EQFT), which is related to the MillerRabin test and the Quadratic
Frobenius test (QFT) by Grantham. EQFT takes time about equivalent to 2
MillerRabin tests, but has much smaller error probability, namely
for iterations of the test in the worst case. EQFT extends
QFT by verifying additional algebraic properties related to the existence of
elements of order dividing 24. We also give bounds on the averagecase
behaviour of the test: consider the algorithm that repeatedly chooses random
odd bit numbers, subjects them to iterations of our test and outputs
the first one found that passes all tests. We obtain numeric upper bounds for
the error probability of this algorithm as well as a general closed
expression bounding the error. For instance, it is at most for
.
 RS038

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PDF,
DVI.
Ivan B. Damgård and Gudmund Skovbjerg
Frandsen.
Efficient Algorithms for gcd and Cubic Residuosity in the Ring
of Eisenstein Integers.
February 2003.
11 pp. Appears in Lingas and Nilsson, editors, Fundamentals of
Computation Theory: 14th International Conference, FCT '03 Proceedings,
LNCS 2751, 2003, pages 109117.
Abstract: We present simple and efficient algorithms for
computing gcd and cubic residuosity in the ring of Eisenstein integers,
, i.e. the integers extended with , a complex primitive
third root of unity. The algorithms are similar and may be seen as
generalisations of the binary integer gcd and derived Jacobi symbol
algorithms. Our algorithms take time for bit input. This is an
improvement from the known results based on the Euclidian algorithm, and
taking time , where denotes the complexity of
multipliplying bit integers. The new algorithms have applications in
practical primality tests and the implementation of cryptographic protocols.
The technique underlying our algorithms can be used to obtain equally fast
algorithms for gcd and quartic residuosity in the ring of Gaussian integers,
.
 RS037

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PDF,
DVI.
Claus Brabrand, Michael I. Schwartzbach,
and Mads Vanggaard.
The METAFRONT System: Extensible Parsing and Transformation.
February 2003.
24 pp.
Abstract: We present the metafront tool for specifying
flexible, safe, and efficient syntactic transformations between languages
defined by contextfree grammars. The transformations are guaranteed to
terminate and to map grammatically legal input to grammatically legal
output.
We rely on a novel parser algorithm that is designed to
support gradual extensions of a grammar by allowing productions to remain in
a natural style and by statically reporting ambiguities and errors in terms
of individual productions as they are being added.
Our tool may be
used as a parser generator in which the resulting parser automatically
supports a flexible, safe, and efficient macro processor, or as an extensible
lightweight compiler generator for domainspecific languages. We show
substantial examples of both kinds.
 RS036

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PDF.
Giuseppe Milicia and Vladimiro Sassone.
Jeeg: Temporal Constraints for the Synchronization of Concurrent
Objects.
February 2003.
41 pp. Short version appears in Fox and Getov, editors, Joint
ACMISCOPE Conference on Java Grande, JGI '02 Proceedings, 2002, pages
212221.
Abstract: We introduce Jeeg, a dialect of Java based on a
declarative replacement of the synchronization mechanisms of Java that
results in a complete decoupling of the `business' and the `synchronization'
code of classes. Synchronization constraints in Jeeg are expressed in a
linear temporal logic which allows to effectively limit the occurrence of the
inheritance anomaly that commonly affects concurrent object oriented
languages. Jeeg is inspired by the current trend in aspect oriented
languages. In a Jeeg program the sequential and concurrent aspects of object
behaviors are decoupled: specified separately by the programmer these are
then weaved together by the Jeeg compiler.
 RS035

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PDF.
Aske Simon Christensen, Anders Møller,
and Michael I. Schwartzbach.
Precise Analysis of String Expressions.
February 2003.
15 pp.
Abstract: We perform static analysis of Java programs to answer
a simple question: which values may occur as results of string expressions?
The answers are summarized for each expression by a regular language that is
guaranteed to contain all possible values. We present several applications of
this analysis, including statically checking the syntax of dynamically
generated expressions, such as SQL queries. Our analysis constructs flow
graphs from class files and generates a contextfree grammar with a
nonterminal for each string expression. The language of this grammar is then
widened into a regular language through a variant of an algorithm previously
used for speech recognition. The collection of resulting regular languages is
compactly represented as a special kind of multilevel automaton from which
individual answers may be extracted. If a program error is detected, examples
of invalid strings are automatically produced. We present extensive
benchmarks demonstrating that the analysis is efficient and produces results
of useful precision.
 RS034

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PDF,
DVI.
Marco Carbone, Mogens Nielsen, and
Vladimiro Sassone.
A Formal Model for Trust in Dynamic Networks.
January 2003.
18 pp. Appears in Cerone and Lindsay, editors, 1st International
Conference on Software Engineering and Formal Methods, SEFM '03
Proceedings, 2003, pages 5461.
Abstract: We propose a formal model of trust informed by the
Global Computing scenario and focusing on the aspects of trust formation,
evolution, and propagation. The model is based on a novel notion of trust
structures which, building on concepts from trust management and domain
theory, feature at the same time a trust and an information partial order.
 RS033

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PDF.
Claude Crépeau, Paul Dumais, Dominic
Mayers, and Louis Salvail.
On the Computational Collapse of Quantum Information.
January 2003.
31 pp.
Abstract: We analyze the situation where computationally
binding string commitment schemes are used to force the receiver of a BB84
encoding of a classical bitstring to measure upon reception. Since measuring
induces an irreversible collapse to the received quantum state, even given
extra information after the measurement does not allow the receiver to
evaluate reliably some predicates apply to the classical bits encoded in the
state. This fundamental quantum primitive is called quantum measure
commitment (QMC) and allows for secure twoparty computation of classical
functions. An adversary to QMC is one that can both provide valid proof of
having measured the received states while still able to evaluate a predicate
applied to the classical content of the encoding. We give the first quantum
blackbox reduction for the security of QMC to the binding property of the
string commitment. We characterize a class of quantum adversaries against QMC
that can be transformed into adversaries against a weak form for the binding
property of the string commitment. Our result provides a construction for
oblivious transfer that is computationally secure against the receiver
and unconditionally secure against the sender from any string commitment
scheme satisfying a weak binding property.
 RS032

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PDF,
DVI.
Olivier Danvy and Pablo E. Martínez
López.
Tagging, Encoding, and Jones Optimality.
January 2003.
Appears in Degano, editor, Programming Languages and Systems:
Twelfth European Symposium on Programming, ESOP '03 Proceedings,
LNCS 2618, 2003, pages 335347.
Abstract: A partial evaluator is said to be Jonesoptimal if
the result of specializing a selfinterpreter with respect to a source
program is textually identical to the source program, modulo renaming. Jones
optimality has already been obtained if the selfinterpreter is untyped. If
the selfinterpreter is typed, however, residual programs are cluttered with
type tags. To obtain the original source program, these tags must be
removed.
A number of sophisticated solutions have already been
proposed. We observe, however, that with a simple representation shift,
ordinary partial evaluation is already Jonesoptimal, modulo an encoding. The
representation shift amounts to reading the type tags as constructors for
higherorder abstract syntax. We substantiate our observation by considering
a typed selfinterpreter whose input syntax is higherorder. Specializing
this interpreter with respect to a source program yields a residual program
that is textually identical to the source program, modulo renaming.
 RS031

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PDF,
DVI.
Vladimiro Sassone and Pawe Sobocinski.
Deriving Bisimulation Congruences: 2Categories vs. Precategories.
January 2003.
28 pp. Appears in Gordon, editor, Foundations of Software
Science and Computation Structures, FoSSaCS '03 Proceedings, LNCS 2620,
2003, pages 409424.
Abstract: Grelative pushouts (GRPOs) have recently been
proposed by the authors as a new foundation for Leifer and Milner's approach
to deriving labelled bisimulation congruences from reduction systems. This
paper develops the theory of GRPOs further, arguing that they provide a
simple and powerful basis towards a comprehensive solution. As an example, we
construct GRPOs in a category of `bunches and wirings.' We then examine the
approach based on Milner's precategories and Leifer's functorial reactive
systems, and show that it can be recast in a much simpler way into the
2categorical theory of GRPOs.
