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This paper defines some "weakest precondltmn'" predicate transformers, Investigates their "healthiness" properties, and apphes them to Dljkstra's language of guarded commands It shows that Dljkstra's w~ function is not the weakest healthy one, but it ~s clearly the best one for practical programming, because it proves the absence of bhnd alleys from a nondetermmlsac program
C. A. R. Hoare (Sat,) studied this question.