3,434 research outputs found
A Focused Sequent Calculus Framework for Proof Search in Pure Type Systems
Basic proof-search tactics in logic and type theory can be seen as the
root-first applications of rules in an appropriate sequent calculus, preferably
without the redundancies generated by permutation of rules. This paper
addresses the issues of defining such sequent calculi for Pure Type Systems
(PTS, which were originally presented in natural deduction style) and then
organizing their rules for effective proof-search. We introduce the idea of
Pure Type Sequent Calculus with meta-variables (PTSCalpha), by enriching the
syntax of a permutation-free sequent calculus for propositional logic due to
Herbelin, which is strongly related to natural deduction and already well
adapted to proof-search. The operational semantics is adapted from Herbelin's
and is defined by a system of local rewrite rules as in cut-elimination, using
explicit substitutions. We prove confluence for this system. Restricting our
attention to PTSC, a type system for the ground terms of this system, we obtain
the Subject Reduction property and show that each PTSC is logically equivalent
to its corresponding PTS, and the former is strongly normalising iff the latter
is. We show how to make the logical rules of PTSC into a syntax-directed system
PS for proof-search, by incorporating the conversion rules as in
syntax-directed presentations of the PTS rules for type-checking. Finally, we
consider how to use the explicitly scoped meta-variables of PTSCalpha to
represent partial proof-terms, and use them to analyse interactive proof
construction. This sets up a framework PE in which we are able to study
proof-search strategies, type inhabitant enumeration and (higher-order)
unification
Using Extended Tactics to Do Proof Transformations
In this thesis we develop a comprehensive human-oriented theorem proving system that integrates several different proof systems. The main theorem proving environment centers around a natural Gentzen first-order logic system. This allows construction of natural proofs, encourages user involvement in the search for proofs, and facilitates understanding of the resulting proofs. We integrate more abstract automatically generated proofs such as resolution refutations by transforming them to proofs in the Gentzen system. Expansion trees are another proof system used as an intermediate stage in transformations between the abstract and natural systems. They are a compact representation useful for transformations and other computations. We develop a programming language approach to theorem proving based on tactics and tacticals. Our extended tactics provide a method for doing proof transformations, as well as facilitate interactive theorem proving, allowing full integration of interactive and automatic theorem proving. In the system, we explicitly represent proofs in each proof system and view expansion tree proofs as types for Gentzen proof terms. This explicit proof representation allows proofs to be manipulated as meaningful data objects and used in various computations. For example, the proof terms in the natural Gentzen system can be used to obtain natural language explanations of proofs. We foresee several applications for this kind of theorem proving system, such as use as a logic tutor, a tool for doing mathematics, or an enhanced reasoner and explanation facility for existing A1 systems
Towards an Intelligent Tutor for Mathematical Proofs
Computer-supported learning is an increasingly important form of study since
it allows for independent learning and individualized instruction. In this
paper, we discuss a novel approach to developing an intelligent tutoring system
for teaching textbook-style mathematical proofs. We characterize the
particularities of the domain and discuss common ITS design models. Our
approach is motivated by phenomena found in a corpus of tutorial dialogs that
were collected in a Wizard-of-Oz experiment. We show how an intelligent tutor
for textbook-style mathematical proofs can be built on top of an adapted
assertion-level proof assistant by reusing representations and proof search
strategies originally developed for automated and interactive theorem proving.
The resulting prototype was successfully evaluated on a corpus of tutorial
dialogs and yields good results.Comment: In Proceedings THedu'11, arXiv:1202.453
Hyper Natural Deduction
Paper introduces a Hyper Natural Deduction system as an extension of Gentzen's Natural Deduction system, by adding additional rules providing means for communication between derivations. It is shown that the Hyper Natural Deduction system is sound and complete for infinite-valued propositional Gödel Logic, by giving translations to and from Avron's Hyper sequent Calculus. The paper also provides conversions for normalisation and prove the existence of normal forms for the Hyper Natural Deduction system
NATURAL DEDUCTION AS HIGHER-ORDER RESOLUTION
An interactive theorem prover, Isabelle, is under development. In LCF, each
inference rule is represented by one function for forwards proof and another (a
tactic) for backwards proof. In Isabelle, each inference rule is represented by
a Horn clause. Resolution gives both forwards and backwards proof, supporting a
large class of logics. Isabelle has been used to prove theorems in
Martin-L\"of's Constructive Type Theory. Quantifiers pose several difficulties:
substitution, bound variables, Skolemization. Isabelle's representation of
logical syntax is the typed lambda-calculus, requiring higher- order
unification. It may have potential for logic programming. Depth-first
subgoaling along inference rules constitutes a higher-order Prolog
Decidability for Non-Standard Conversions in Typed Lambda-Calculi
This thesis studies the decidability of conversions in typed lambda-calculi, along with the algorithms allowing for this decidability. Our study takes in consideration conversions going beyond the traditional beta, eta, or permutative conversions (also called commutative conversions). To decide these conversions, two classes of algorithms compete, the algorithms based on rewriting, here the goal is to decompose and orient the conversion so as to obtain a convergent system, these algorithms then boil down to rewrite the terms until they reach an irreducible forms; and the "reduction free" algorithms where the conversion is decided recursively by a detour via a meta-language. Throughout this thesis, we strive to explain the latter thanks to the former
- …