Wilmer Ricciotti

A web interface for matita

This article describes a prototype implementation of a web interface for the Matita proof assistant [2]. The motivations behind our work are similar to those of several recent, related efforts [7,9,1,8] (see also [6]).

The Matita interactive theorem prover

Matita is an interactive theorem prover being developed by the Helm team at the University of Bologna. Its stable version 0.5.x may be downloaded at http://matita.cs.unibo.it. The tool originated in the European project MoWGLI as a set of XML-based tools aimed to provide a mathematician-friendly web-interface to repositories of formal mathematical knoweldge, supporting advanced content-based functionalities for querying, searching and browsing the library. It has since then evolved into a fully fledged ITP, specifically designed as a light-weight, but competitive system, particularly suited for the assessment of innovative ideas, both at foundational and logical level. In this paper, we give an account of the whole system, its peculiarities and its main applications.

Hints in Unification

Several mechanisms such as Canonical Structures [14], Type Classes [13,16], or Pullbacks [10] have been recently introduced with the aim to improve the power and flexibility of the type inference algorithm for interactive theorem provers. We claim that all these mechanisms are particular instances of a simpler and more general technique, just consisting in providing suitable hints to the unification procedure underlying type inference. This allows a simple, modular and not intrusive implementation of all the above mentioned techniques, opening at the same time innovative and unexpected perspectives on its possible applications.

About the Formalization of Some Results by Chebyshev in Number Theory

We discuss the formalization, in the Matita Interactive Theorem Prover, of a famous result by Chebyshev concerning the distribution of prime numbers, essentially subsuming, as a corollary, Bertrands postulate. Even if Chebyshevs result has been later superseded by the stronger prime number theorem, his machinery, and in particular the two functions *** and *** still play a central role in the modern development of number theory. Differently from other recent formalizations of other results in number theory, our proof is entirely arithmetical. It makes use of most part of the machinery of elementary arithmetics, and in particular of properties of prime numbers, factorization, products and summations, providing a natural benchmark for assessing the actual development of the arithmetical knowledge base.

Formalizing Turing Machines

We discuss the formalization, in the Matita Theorem Prover, of a few, basic results on Turing Machines, up to the existence of a (certified) Universal Machine. The work is meant to be a preliminary step towards the creation of a formal repository in Complexity Theory, and is a small piece in our Reverse Complexity program, aiming to a comfortable, machine independent axiomatization of the field.

A formalization of multi-tape Turing machines

We discuss the formalization, in the Matita Theorem Prover, of basic results on multi-tapes Turing machines, up to the existence of a (certified) Universal Machine, and propose it as a natural benchmark for comparing different interactive provers and assessing the state of the art in the mechanization of formal reasoning. The work is meant to be a preliminary step towards the creation of a formal repository in Complexity Theory, and is a small piece in our long-term Reverse Complexity program, aiming to a comfortable, machine independent axiomatization of the field.

Formal Metatheory of Programming Languages in the Matita Interactive Theorem Prover

This paper is a report about the use of Matita, an interactive theorem prover under development at the University of Bologna, for the solution of the POPLmark Challenge, part 1a. We provide three different formalizations, including two direct solutions using pure de Bruijn and locally nameless encodings of bound variables, and a formalization using named variables, obtained by means of a sound translation to the locally nameless encoding. According to this experience, we also discuss some of the proof principles used in our solutions, which have led to the development of a generalized inversion tactic for Matita.

Imperative functional programs that explain their work

Program slicing provides explanations that illustrate how program outputs were produced from inputs. We build on an approach introduced in prior work, where dynamic slicing was defined for pure higher-order functional programs as a Galois connection between lattices of partial inputs and partial outputs. We extend this approach to imperative functional programs that combine higher-order programming with references and exceptions. We present proofs of correctness and optimality of our approach and a proof-of-concept implementation and experimental evaluation.

Strongly Normalizing Audited Computation

Auditing is an increasingly important operation for computer programming, for example in security (e.g. to enable history-based access control) and to enable reproducibility and accountability (e.g. provenance in scientific programming). Most proposed auditing techniques are ad hoc or treat auditing as a second-class, extralinguistic operation; logical or semantic foundations for auditing are not yet well-established. Justification Logic (JL) offers one such foundation; Bavera and Bonelli introduced a computational interpretation of JL called lambda^h that supports auditing. However, lambda^h is technically complex and strong normalization was only established for special cases. In addition, we show that the equational theory of lambda^h is inconsistent. We introduce a new calculus lambda^hc that is simpler than lambda^hc, consistent, and strongly normalizing. Our proof of strong normalization is formalized in Nominal Isabelle.

A core calculus for provenance inspection

Recent research has been devoting increasing attention to provenance, or information describing the origin, derivation, and history of data, due to its relevance to critical issues including transparency, privacy, and security. Engineering a software system to make it provenance-aware by means of ad-hoc instrumentation requires a substantial effort: the development of general-purpose infrastructure is thus very important to achieve the goal of making provenance widely available. In this article we describe a core functional language equipped with a provenance-aware semantics that is sufficiently generic to accomodate many notions of provenance proposed in the literature. While existing proposals typically treat provenance views and provenance extraction as second-class, extralinguistic mechanisms, in our work provenance views are expressed as standard programs and provenance data can be reflected into the language, allowing for programs that inspect their own provenance.