4 research outputs found
Recent Advances in Σ-definability over Continuous Data Types
The purpose of this paper is to survey our recent research in computability and definability over continuous data types such as the real numbers, real-valued functions and functionals. We investigate the expressive power and algorithmic properties of the language of Sigma-formulas intended to represent computability over the real numbers. In order to adequately represent computability we extend the reals by the structure of hereditarily finite sets. In this setting it is crucial to consider the real numbers without equality since the equality test is undecidable over the reals. We prove Engeler's Lemma for Sigma-definability over the reals without the equality test which relates Sigma-definability with definability in the constructive infinitary language L_{omega_1 omega}. Thus, a relation over the real numbers is Sigma-definable if and only if it is definable by a disjunction of a recursively enumerable set of quantifier free formulas. This result reveals computational aspects of Sigma-definability and also gives topological characterisation of Sigma-definable relations over the reals without the equality test. We also illustrate how computability over the real numbers can be expressed in the language of Sigma-formulas
A Proof Planning Framework For Isabelle
Centre for Intelligent Systems and their ApplicationsProof planning is a paradigm for the automation of proof that focuses on encoding intelligence
to guide the proof process. The idea is to capture common patterns of reasoning which can be
used to derive abstract descriptions of proofs known as proof plans. These can then be executed
to provide fully formal proofs.
This thesis concerns the development and analysis of a novel approach to proof planning
that focuses on an explicit representation of choices during search. We embody our approach
as a proof planner for the generic proof assistant Isabelle and use the Isar language, which is
human-readable and machine-checkable, to represent proof plans. Within this framework we
develop an inductive theorem prover as a case study of our approach to proof planning.
Our prover uses the difference reduction heuristic known as rippling to automate the step
cases of the inductive proofs. The development of a flexible approach to rippling that supports
its various modifications and extensions is the second major focus of this thesis. Here, our
inductive theorem prover provides a context in which to evaluate rippling experimentally.
This work results in an efficient and powerful inductive theorem prover for Isabelle as well
as proposals for further improving the efficiency of rippling. We also draw observations in order
to direct further work on proof planning. Overall, we aim to make it easier for mathematical
techniques, and those specific to mechanical theorem proving, to be encoded and applied to
problems