128 research outputs found
Mechanising syntax with binders in Coq
Mechanising binders in general-purpose proof assistants such as Coq is cumbersome and difficult. Yet binders, substitutions, and instantiation of terms with substitutions are a critical ingredient of many programming languages. Any practicable mechanisation of the meta-theory of the latter hence requires a lean formalisation of the former. We investigate the topic from three angles: First, we realise formal systems with binders based on both pure and scoped de Bruijn algebras together with basic syntactic rewriting lemmas and automation. We automate this process in a compiler called Autosubst; our final tool supports many-sorted, variadic, and modular syntax. Second, we justify our choice of realisation and mechanise a proof of convergence of the sigma calculus, a calculus of explicit substitutions that is complete for equality of the de Bruijn algebra corresponding to the lambda calculus. Third, to demonstrate the practical usefulness of our approach, we provide concise, transparent, and accessible mechanised proofs for a variety of case studies refined to de Bruijn substitutions.Die Mechanisierung von Bindern in universellen Beweisassistenten wie Coq ist arbeitsaufwÀndig und schwierig. Binder, Substitutionen und die Instantiierung von Substitutionen sind jedoch kritischer Bestandteil
vieler Programmiersprachen. Deshalb setzt eine praktikable Mechanisierung der Metatheorie von Programmiersprachen eine elegante Formalisierung von Bindern voraus. Wir nÀhern uns dem Thema aus drei Richtungen an:
Zuerst realisieren wir formale Systeme mit Bindern mit Hilfe von reinen und indizierten de Bruijn Algebren, zusammen mit grundlegenden syntaktischen Gleichungen und Automatisierung. Wir automatisieren diesen Prozess in
einem Kompilierer namens Autosubst. Unser finaler Kompilierer unterstĂŒtzt Sortenlogik, variadische Syntax und modulare Syntax. Zweitens rechtfertigen wir unsere ReprĂ€sentation und mechanisieren einen Beweis der Konvergenz
des SP-KalkĂŒls, einem KalkĂŒl expliziter Substitutionen der bezĂŒglich der Gleichheit der puren de Bruijn Algebra des -KalkĂŒls vollstĂ€ndig ist. Drittens entwickeln wir kurze, transparente und leicht zugĂ€ngliche mechanisierte
Beweise fĂŒr diverse Fallstudien, die wir an de Bruijn Substitutionen angepasst haben. Wir weisen so die praktische Anwendbarkeit unseres Ansatzes nach
The Theory of LEGO
LEGO is a computer program for interactive typechecking in the Extended Calculus of Constructions and two of its subsystems. LEGO also supports the extension of these three systems with inductive types. These type systems can be viewed as logics, and as meta languages for expressing logics, and LEGO is intended to be used for interactively constructing proofs in mathematical theories presented in these logics. I have developed LEGO over six years, starting from an implementation of the Calculus of Constructions by GĂ©rard Huet. LEGO has been used for problems at the limits of our abilities to do formal mathematics.
In this thesis I explain some aspects of the meta-theory of LEGO's type systems leading to a machine-checked proof that typechecking is decidable for all three type theories supported by LEGO, and to a verified algorithm for deciding their typing judgements, assuming only that they are normalizing. In order to do this, the theory of Pure Type Systems (PTS) is extended and formalized in LEGO. This extended example of a formally developed body of mathematics is described, both for its main theorems, and as a case study in formal mathematics. In many examples, I compare formal definitions and theorems with their informal counterparts, and with various alternative approaches, to study the meaning and use of mathematical language, and suggest clarifications in the informal usage.
Having outlined a formal development far too large to be surveyed in detail by a human reader, I close with some thoughts on how the human mathematician's state of understanding and belief might be affected by possessing such a thing
POPLMark reloaded: Mechanizing proofs by logical relations
We propose a new collection of benchmark problems in mechanizing the metatheory of programming languages, in order to compare and push the state of the art of proof assistants. In particular, we focus on proofs using logical relations (LRs) and propose establishing strong normalization of a simply typed calculus with a proof by Kripke-style LRs as a benchmark. We give a modern view of this well-understood problem by formulating our LR on well-typed terms. Using this case study, we share some of the lessons learned tackling this problem in different dependently typed proof environments. In particular, we consider the mechanization in Beluga, a proof environment that supports higher-order abstract syntax encodings and contrast it to the development and strategies used in general-purpose proof assistants such as Coq and Agda. The goal of this paper is to engage the community in discussions on what support in proof environments is needed to truly bring mechanized metatheory to the masses and engage said community in the crafting of future benchmarks
Comparing Calculi of Explicit Substitutions with Eta-reduction1 1Partially supported by the Brazilian CNPq research council grant number 47488101-6.
AbstractThe past decade has seen an explosion of work on calculi of explicit substitutions. Numerous work has illustrated the usefulness of these calculi for practical notions like the implementation of typed functional programming languages and higher order proof assistants. Three styles of explicit substitutions are treated in this paper: the Î»Ï and the λse which have proved useful for solving practical problems like higher order unification, and the suspension calculus related to the implementation of the language λ-Prolog. We enlarge the suspension calculus with an adequate eta-reduction which we show to preserve termination and confluence of the associated substitution calculus and to correspond to the eta-reductions of the other two calculi. Additionally, we prove that Î»Ï and λse as well as Î»Ï and the suspension calculus are non comparable while λse is more adequate than the suspension calculus
Union, intersection, and refinement types and reasoning about type disjointness for security protocol analysis
In this thesis we present two new type systems for verifying the security of cryptographic protocol models expressed in a spi-calculus and, respectively, of protocol implementations expressed in a concurrent lambda calculus. In this thesis we present two new type systems for verifying the security of cryptographic protocol models expressed in a spi-calculus and, respectively, of protocol implementations expressed in a concurrent lambda calculus. The two type systems combine prior work on refinement types with union and intersection types and with the novel ability to reason statically about the disjointness of types. The increased expressivity enables the analysis of important protocol classes that were previously out of scope for the type-based analyses of cryptographic protocols. In particular, our type systems can statically analyze protocols that are based on zero-knowledge proofs, even in scenarios when certain protocol participants are compromised. The analysis is scalable and provides security proofs for an unbounded number of protocol executions. The two type systems come with mechanized proofs of correctness and efficient implementations.In dieser Arbeit werden zwei neue Typsysteme vorgestellt, mit denen die Sicherheit kryptographischer Protokolle, modelliert in einem spi-KalkĂŒl, und Protokollimplementierungen, beschrieben in einem nebenlĂ€ufigen LambdakalkĂŒl, verifiziert werden kann. Die beiden Typsysteme verbinden vorausgehende Arbeiten zu Verfeinerungstypen mit disjunktiven und konjunktiven Typen, und ermöglichen auĂerdem, statisch zu folgern, dass zwei Typen disjunkt sind. Die AusdrucksstĂ€rke der Systeme erlaubt die Analyse wichtiger Klassen von Protokollen, die bisher nicht durch typbasierte Protokollanalysen behandelt werden konnten. Insbesondere ist mit den vorgestellten Typsystemen auch die statische Analyse von Protokollen möglich, die auf Zero-Knowledge-Beweisen basieren, selbst unter der Annahme, dass einige Protokollteilnehmer korrumpiert sind. Die Analysetechnik skaliert und erlaubt Sicherheitsbeweise fĂŒr eine unbeschrĂ€nkte Anzahl von ProtokollausfĂŒhrungen. Die beiden Typsysteme sind formal korrekt bewiesen und effizient implementiert
Spartan Daily, February 15, 1990
Volume 94, Issue 14https://scholarworks.sjsu.edu/spartandaily/7944/thumbnail.jp
Spartan Daily, February 15, 1990
Volume 94, Issue 14https://scholarworks.sjsu.edu/spartandaily/7944/thumbnail.jp
Adventures in Formalisation: Financial Contracts, Modules, and Two-Level Type Theory
We present three projects concerned with applications of proof assistants in
the area of programming language theory and mathematics. The first project is
about a certified compilation technique for a domain-specific programming
language for financial contracts (the CL language). The code in CL is
translated into a simple expression language well-suited for integration with
software components implementing Monte Carlo simulation techniques (pricing
engines). The compilation procedure is accompanied with formal proofs of
correctness carried out in Coq. The second project presents techniques that
allow for formal reasoning with nested and mutually inductive structures built
up from finite maps and sets. The techniques, which build on the theory of
nominal sets combined with the ability to work with isomorphic representations
of finite maps, make it possible to give a formal treatment, in Coq, of a
higher-order module system, including the ability to eliminate at compile time
abstraction barriers introduced by the module system. The development is based
on earlier work on static interpretation of modules and provides the foundation
for a higher-order module language for Futhark, an optimising compiler
targeting data-parallel architectures. The third project presents an
implementation of two-level type theory, a version of Martin-Lof type theory
with two equality types: the first acts as the usual equality of homotopy type
theory, while the second allows us to reason about strict equality. In this
system, we can formalise results of partially meta-theoretic nature. We develop
and explore in details how two-level type theory can be implemented in a proof
assistant, providing a prototype implementation in the proof assistant Lean. We
demonstrate an application of two-level type theory by developing some results
on the theory of inverse diagrams using our Lean implementation.Comment: PhD thesis defended in January 2018 at University of Copenhagen,
Department of Computer Scienc
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