CARIBOO: A Multi-Strategy Termination Proof Tool Based on Induction
Résumé
We describe Cariboo, the implementation of an inductive process recently proposed to prove termination of rewriting under strategies on ground term algebras. The method is based on an abstraction mechanism, introducing variables that represent ground terms in normal form, and on narrowing, schematizing reductions on ground terms. It applies in particular to non-terminating systems which are terminating with innermost, outermost or local strategies. The narrowing process, well known to easily diverge, is controlled by using appropriate abstraction constraints. The abstraction mechanism lies on satisfiability of ordering constraints. Thanks to the power of induction, these ordering constraints are often simple and automatically solved by our system. Otherwise, they can be treated by the user or any external automatic solver. On many examples, Cariboo even enables to succeed without considering any constraint at all~\,; the process is then completely automatic. Cariboo offers a graphical view of the proof process. It is implemented in ELAN, a rule based programming environment, and so can be used for proving termination of ELAN programs.