5,551 research outputs found
Formalising Mathematics in Simple Type Theory
Despite the considerable interest in new dependent type theories, simple type
theory (which dates from 1940) is sufficient to formalise serious topics in
mathematics. This point is seen by examining formal proofs of a theorem about
stereographic projections. A formalisation using the HOL Light proof assistant
is contrasted with one using Isabelle/HOL. Harrison's technique for formalising
Euclidean spaces is contrasted with an approach using Isabelle/HOL's axiomatic
type classes. However, every formal system can be outgrown, and mathematics
should be formalised with a view that it will eventually migrate to a new
formalism
Applying formal methods to standard development: the open distributed processing experience
Since their introduction, formal methods have been applied in various ways to different standards. This paper gives an account of these applications, focusing on one application in particular: the development of a framework for creating standards for Open Distributed Processing (ODP). Following an introduction to ODP, the paper gives an insight into the current work on formalising the architecture of the
Reference Model of ODP (RM-ODP), highlighting the advantages to be gained. The different approaches currently being taken are shown, together with their associated advantages and disadvantages. The paper concludes that there is no one all-purpose approach which can be used
in preference to all others, but that a combination of approaches is desirable to best fulfil the potential of formal methods in developing an architectural semantics for OD
Inductive and Coinductive Components of Corecursive Functions in Coq
In Constructive Type Theory, recursive and corecursive definitions are
subject to syntactic restrictions which guarantee termination for recursive
functions and productivity for corecursive functions. However, many terminating
and productive functions do not pass the syntactic tests. Bove proposed in her
thesis an elegant reformulation of the method of accessibility predicates that
widens the range of terminative recursive functions formalisable in
Constructive Type Theory. In this paper, we pursue the same goal for productive
corecursive functions. Notably, our method of formalisation of coinductive
definitions of productive functions in Coq requires not only the use of ad-hoc
predicates, but also a systematic algorithm that separates the inductive and
coinductive parts of functions.Comment: Dans Coalgebraic Methods in Computer Science (2008
Theorem of three circles in Coq
The theorem of three circles in real algebraic geometry guarantees the
termination and correctness of an algorithm of isolating real roots of a
univariate polynomial. The main idea of its proof is to consider polynomials
whose roots belong to a certain area of the complex plane delimited by straight
lines. After applying a transformation involving inversion this area is mapped
to an area delimited by circles. We provide a formalisation of this rather
geometric proof in Ssreflect, an extension of the proof assistant Coq,
providing versatile algebraic tools. They allow us to formalise the proof from
an algebraic point of view.Comment: 27 pages, 5 figure
Applying G\"odel's Dialectica Interpretation to Obtain a Constructive Proof of Higman's Lemma
We use G\"odel's Dialectica interpretation to analyse Nash-Williams' elegant
but non-constructive "minimal bad sequence" proof of Higman's Lemma. The result
is a concise constructive proof of the lemma (for arbitrary decidable
well-quasi-orders) in which Nash-Williams' combinatorial idea is clearly
present, along with an explicit program for finding an embedded pair in
sequences of words.Comment: In Proceedings CL&C 2012, arXiv:1210.289
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Formalising Engineering Judgement on Software Dependability via Belief Networks
Informal proof, formal proof, formalism
Increases in the use of automated theorem-provers have renewed focus on the relationship between the informal proofs normally found in mathematical research and fully formalised derivations. Whereas some claim that any correct proof will be underwritten by a fully formal proof, sceptics demur. In this paper I look at the relevance of these issues for formalism, construed as an anti-platonistic metaphysical doctrine. I argue that there are strong reasons to doubt that all proofs are fully formalisable, if formal proofs are required to be finitary, but that, on a proper view of the way in which formal proofs idealise actual practice, this restriction is unjustified and formalism is not threatened
Coinductive Formal Reasoning in Exact Real Arithmetic
In this article we present a method for formally proving the correctness of
the lazy algorithms for computing homographic and quadratic transformations --
of which field operations are special cases-- on a representation of real
numbers by coinductive streams. The algorithms work on coinductive stream of
M\"{o}bius maps and form the basis of the Edalat--Potts exact real arithmetic.
We use the machinery of the Coq proof assistant for the coinductive types to
present the formalisation. The formalised algorithms are only partially
productive, i.e., they do not output provably infinite streams for all possible
inputs. We show how to deal with this partiality in the presence of syntactic
restrictions posed by the constructive type theory of Coq. Furthermore we show
that the type theoretic techniques that we develop are compatible with the
semantics of the algorithms as continuous maps on real numbers. The resulting
Coq formalisation is available for public download.Comment: 40 page
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