Towards Coinductive Theory Exploration in Horn Clause Logic: Position Paper

Coinduction occurs in two guises in Horn clause logic: in proofs of self-referencing properties and relations, and in proofs involving construction of (possibly irregular) infinite data. Both instances of coinductive reasoning appeared in the literature before, but a systematic analysis of these two kinds of proofs and of their relation was lacking. We propose a general proof-theoretic framework for handling both kinds of coinduction arising in Horn clause logic. To this aim, we propose a coinductive extension of Miller et al's framework of uniform proofs and prove its soundness relative to coinductive models of Horn clause logic. Coinductive proof methods have seen major developments in the last decade, and are reaching the point of maturity when coinductive proofs are used and implemented on par with inductive proofs.