27,263 research outputs found
On Solving Word Equations Using SAT
We present Woorpje, a string solver for bounded word equations (i.e.,
equations where the length of each variable is upper bounded by a given
integer). Our algorithm works by reformulating the satisfiability of bounded
word equations as a reachability problem for nondeterministic finite automata,
and then carefully encoding this as a propositional satisfiability problem,
which we then solve using the well-known Glucose SAT-solver. This approach has
the advantage of allowing for the natural inclusion of additional linear length
constraints. Our solver obtains reliable and competitive results and,
remarkably, discovered several cases where state-of-the-art solvers exhibit a
faulty behaviour
The Strategy the Use of False Assumption and Word Problem Solving
The paper describes one problem solving strategy – the Use of false assumption. The objective of the paper is to show, in accordance with Phylogenesis and Ontogenesis Theory, that it is worthwhile to reiterate the process of development of the concept of a variable and thus provide to pupils one of the ways helping them to eliminate usual difficulties when solving word problems using linear equations, namely construction of the equations. The paper presents the outcomes of a study conducted on three lower secondary schools in the Czech Republic with 147 14–15-year-old pupils. Pupils from the experimental group were, unlike pupils from the control group, taught the strategy the Use of false assumption before being taught the topic Solving word problems. The tool for the study was a test of four problems that was sat by all the involved pupils three weeks after finishing the topic “Solving word problems” and whose results were evaluated statistically. The experiment confirmed the research hypothesis that the introduction of the strategy the Use of false assumption into 8th grade mathematics lessons (14–15-year-old pupils) helps pupils construct equations more successfully when solving word problems
Equations over free inverse monoids with idempotent variables
We introduce the notion of idempotent variables for studying equations in
inverse monoids.
It is proved that it is decidable in singly exponential time (DEXPTIME)
whether a system of equations in idempotent variables over a free inverse
monoid has a solution. The result is proved by a direct reduction to solve
language equations with one-sided concatenation and a known complexity result
by Baader and Narendran: Unification of concept terms in description logics,
2001. We also show that the problem becomes DEXPTIME hard , as soon as the
quotient group of the free inverse monoid has rank at least two.
Decidability for systems of typed equations over a free inverse monoid with
one irreducible variable and at least one unbalanced equation is proved with
the same complexity for the upper bound.
Our results improve known complexity bounds by Deis, Meakin, and Senizergues:
Equations in free inverse monoids, 2007.
Our results also apply to larger families of equations where no decidability
has been previously known.Comment: 28 pages. The conference version of this paper appeared in the
proceedings of 10th International Computer Science Symposium in Russia, CSR
2015, Listvyanka, Russia, July 13-17, 2015. Springer LNCS 9139, pp. 173-188
(2015
Small Scale AES Toolbox: Algebraic and Propositional Formulas, Circuit-Implementations and Fault Equations
Cryptography is one of the key technologies ensuring security in the digital
domain. As such, its primitives and implementations have been extensively analyzed both
from a theoretical, cryptoanalytical perspective, as well as regarding their capabilities to
remain secure in the face of various attacks.
One of the most common ciphers, the Advanced Encryption Standard (AES) (thus far)
appears to be secure in the absence of an active attacker. To allow for the testing and
development of new attacks or countermeasures a small scale version of the AES with a
variable number of rounds, number of rows, number of columns and data word size, and a
complexity ranging from trivial up to the original AES was developed.
In this paper we present a collection of various implementations of the relevant small scale
AES versions based on hardware (VHDL and gate-level), algebraic representations (Sage
and CoCoA) and their translations into propositional formulas (in CNF). Additionally, we
present fault attack equations for each version.
Having all these resources available in a single and well structured package allows researchers
to combine these different sources of information which might reveal new patterns or solving
strategies. Additionally, the fine granularity of difficulty between the different small scale
AES versions allows for the assessment of new attacks or the comparison of different attacks
Transfer Function Synthesis without Quantifier Elimination
Traditionally, transfer functions have been designed manually for each
operation in a program, instruction by instruction. In such a setting, a
transfer function describes the semantics of a single instruction, detailing
how a given abstract input state is mapped to an abstract output state. The net
effect of a sequence of instructions, a basic block, can then be calculated by
composing the transfer functions of the constituent instructions. However,
precision can be improved by applying a single transfer function that captures
the semantics of the block as a whole. Since blocks are program-dependent, this
approach necessitates automation. There has thus been growing interest in
computing transfer functions automatically, most notably using techniques based
on quantifier elimination. Although conceptually elegant, quantifier
elimination inevitably induces a computational bottleneck, which limits the
applicability of these methods to small blocks. This paper contributes a method
for calculating transfer functions that finesses quantifier elimination
altogether, and can thus be seen as a response to this problem. The
practicality of the method is demonstrated by generating transfer functions for
input and output states that are described by linear template constraints,
which include intervals and octagons.Comment: 37 pages, extended version of ESOP 2011 pape
A Continuous-Discontinuous Second-Order Transition in the Satisfiability of Random Horn-SAT Formulas
We compute the probability of satisfiability of a class of random Horn-SAT
formulae, motivated by a connection with the nonemptiness problem of finite
tree automata. In particular, when the maximum clause length is 3, this model
displays a curve in its parameter space along which the probability of
satisfiability is discontinuous, ending in a second-order phase transition
where it becomes continuous. This is the first case in which a phase transition
of this type has been rigorously established for a random constraint
satisfaction problem
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