 Abstract:
 Coinduction is a proof rule. It is the dual of induction. It allows reasoning about nonwellfounded structures such as lazy lists or streams and is of particular use for reasoning about equivalences. A central difficulty in the automation of coinductive proof is the choice of a relation (called a bisimulation). We present an automation of coinductive theorem proving. This automation is based on the idea of proof planning. Proof planning constructs the higher level steps in a proof, using knowledge of the general structure of a family of proofs and exploiting this knowledge to control the proof search. Part of proof planning involves the use of failure information to modify the plan by the use of a proof critic which exploits the information gained from the failed proof attempt. Our approach to the problem was to develop a strategy that makes an initial simple guess at a bisimulation and then uses generalisation techniques, motivated by a critic, to refine this guess, so that a larger class of coinductive problems can be automatically verified.The implementation of this strategy has focused on the use of coinduction to prove the equivalence of programs in a small lazy functional language which is similar to Haskell. We have developed a proof plan for coinduction and a critic associated with this proof plan. These have been implemented in CoCLAM, an extended version of CLAM with encouraging results. The planner has been successfully tested on a number of theorems.
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 Bibtex format
 @Misc{EDIINFRR0004,
 author = {
Louise Dennis
and Alan Bundy
and Ian Green
},
 title = {Making a Productive Use of Failure to Generate Witnesses for Coinduction from Divergent Proof Attempts},
 year = 1999,
 }
