Drinker Paradox

The drinker paradox (also known as drinker's principle, drinkers' principle or (the) drinking principle) is a theorem of classical predicate logic, usually stated in natural language as: There is someone in the pub such that, if he is drinking, everyone in the pub is drinking. The actual theorem is

where D is an arbitrary predicate. The paradox was popularised by the mathematical logician Raymond Smullyan, who called it the "drinking principle" in his 1978 book What Is the Name of this Book?

Read more about Drinker Paradox:  Proofs of The Paradox, Discussion, History and Variations

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