Healthiness from Duality

摘要

Healthiness is a good old question in program logics that dates back to Dijkstra. It asks for an intrinsic characterization of those predicate transformers which arise as the (backward) interpretation of a certain class of programs. There are several results known for healthiness conditions: for deterministic programs, nondeterministic ones, probabilistic ones, etc. Building upon our previous works on so-called state-and-effect triangles, we contribute a unified categorical framework for investigating healthiness conditions. This framework is based on a dual adjunction induced by a dualizing object and on our notion of relative Eilenberg-Moore algebra. The latter notion seems interesting in its own right in the context of monads, Lawvere theories and enriched categories.