Extending the Applicability Condition in the Formal System \lambda\delta

The formal system \lambda\delta is a typed lambda calculus derived from \Lambda\infinity, aiming to support the foundations of Mathematics that require an underlying theory of expressions (for example the Minimal Type Theory). The system is developed in the context of the Hypertextual Electronic Library of Mathematics as a machine-checked digital specification, that is not the formal counterpart of previous informal material. The first version of the calculus appeared in 2006 and proved unsatisfactory for some reasons. In this article we present a revised version of the system and we prove three relevant desired properties: the confluence of reduction, the strong normalization of an extended form of reduction, known as the ``big tree'' theorem, and the preservation of validity by reduction. To our knowledge, we are presenting here the first fully machine-checked proof of the ``big tree'' theorem for a calculus that includes \Lambda\infinity

Searching and retrieving in content-based repositories of formal mathematical knowledge

In this thesis, the author presents a query language for an RDF (Resource Description Framework) database and discusses its applications in the context of the HELM project (the Hypertextual Electronic Library of Mathematics). This language aims at meeting the main requirements coming from the RDF community. in particular it includes: a human readable textual syntax and a machine-processable XML (Extensible Markup Language) syntax both for queries and for query results, a rigorously exposed formal semantics, a graph-oriented RDF data access model capable of exploring an entire RDF graph (including both RDF Models and RDF Schemata), a full set of Boolean operators to compose the query constraints, fully customizable and highly structured query results having a 4-dimensional geometry, some constructions taken from ordinary programming languages that simplify the formulation of complex queries. The HELM project aims at integrating the modern tools for the automation of formal reasoning with the most recent electronic publishing technologies, in order create and maintain a hypertextual, distributed virtual library of formal mathematical knowledge. In the spirit of the Semantic Web, the documents of this library include RDF metadata describing their structure and content in a machine-understandable form. Using the author's query engine, HELM exploits this information to implement some functionalities allowing the interactive and automatic retrieval of documents on the basis of content-aware requests that take into account the mathematical nature of these documents

Implementing Type Theory in Higher Order Constraint Logic Programming

International audienceIn this paper we are interested in high-level programming languages to implement the core components of an interactive theorem prover for a dependently typed language: the kernel — responsible for type-checking closed terms — and the elaborator — that manipulates terms with holes or, equivalently, partial proof terms. In the first part of the paper we confirm that λProlog, the language developed by Miller and Nadathur since the 80s, is extremely suitable for implementing the kernel, even when efficient techniques like reduction machines are employed. In the second part of the paper we turn our attention to the elaborator and we observe that the eager generative semantics inherited by Prolog makes it impossible to reason by induction over terms containing metavariables. We also conclude that the minimal extension to λProlog that allows to do so is the possibility to delay inductive predicates over flexible terms, turning them into (set of) constraints to be propagated according to user provided constraint propagation rules. Therefore we propose extensions to λProlog to declare and manipulate higher order constraints, and we implement the proposed extensions in the ELPI system. Our test case is the implementation of an elaborator for a type theory as a CLP extension to a kernel written in plain λProlog

ELPI: fast, Embeddable, λProlog Interpreter

International audienceWe present a new interpreter for λProlog that runs consistently faster than the byte code compiled by Teyjus, that is believed to be the best available implementation of λProlog. The key insight is the identification of a fragment of the language, which we call reduction-free fragment (L β λ), that occurs quite naturally in λProlog programs and that admits constant time reduction and unification rules

Il terzo teorema di Godel-Kreisel nella teoria intuizionistica dei tipi di Martin-Lof

The completeness of the fragment strongly denied in intuitionistic logic with respect to the intuitive semantics implies the validity of the principle of Markov in metalanguage where "intuitive semantics 'and' a free translation of naive semantics. This thesis will prove that this theorem can 'be effectively formulated and proved in the intuitionistic theory of types of P. Martin-Lof (ITT), which is exposed in detail in [MLS] and [NPS

Standardization and Confluence in Pure Lambda-Calculus Formalized for the Matita Theorem Prover

We present a formalization of pure ?-calculus for the Matita interactive theorem prover, including the proofs of two relevant results in reduction theory: the confluence theorem and the standardization theorem. The proof of the latter is based on a new approach recently introduced by Xi and refined by Kashima that, avoiding the notion of development and having a neat inductive structure, is particularly suited for formalization in theorem provers

Verified Representations of Landau's "Grundlagen" in the lambda-delta Family and in the Calculus of Constructions

Landau's "Grundlagen der Analysis" formalized in the language Aut-QE, represents an early milestone in computer-checked mathematics and is the only non-trivial development finalized in the languages of the Automath family. Here we discuss an implemented procedure producing a faithful representation of the Grundlagen in the Calculus of Constructions, verified by the proof assistant Coq 8.4.3. The point at issue is distinguishing lambda-abstractions from pi-abstractions where the original text uses Automath unified binders, taking care of the cases in which a binder corresponds to both abstractions at one time. It is a fact that some binders can be disambiguated only by verifying the Grundlagen in a calculus accepting Aut-QE and the Calculus of Constructions. To this end, we rely on lambda-delta version 3, a system that the author is proposing here for the first time

λ-Types on the λ-Calculus with Abbreviations: a Certified Specification

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