Practical Theory Extension in Event-B

Abstract. The Rodin tool for Event-B supports formal modelling and proof using a mathematical language that is based on predicate logic and set theory. Although Rodin has in-built support for a rich set of operators and proof rules, for some application areas there may be a need to extend the set of operators and proof rules supported by the tool. This paper outlines a new feature of the Rodin tool, the theory component, that allows users to extend the mathematical language supported by the tool. Using theories, Rodin users may define new data types and polymorphic operators in a systematic and practical way. Theories also allow users to extend the proof capabilities of Rodin by defining new proof rules that get incorporated into the proof mechanisms. Soundness of new definitions and rules is provided through validity proof obligations.

Building and Executing Proof Strategies in a Formal Metatheory

This paper describes how "safe" proof strategies are represented and executed in the interactive theorem prover GETFOL. A formal metatheory (MT) describes and allows to reason about object level inference. A class of MT terms, called logic tactics, is used to represent proof strategies. The semantic attachment facility and the evaluation mechanism of the GETFOL system have been used to provide the procedural interpretation of logic tactics. The execution of logic tactics is then proved to be "safe" under the termination condition. The implementation within the GETFOL system is described and the synthesis of a logic tactic implementing a normalizer in negative normal form is presented as a case study. 1 Introduction As pointed out in [GMMW77], interactive theorem proving [GMW79, CAB + 86, Pau89] has been growing up in the continuum existing between proof checking [deB70, Wey80] on one side and automated theorem proving [Rob65, And81, Bib81] on the other. Interactive theorem..