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Definition 2024
Peirce's_law
Peirce's law
English
Noun
- (logic) The classically valid but intuitionistically non-valid formula of propositional calculus, which can be used as an substitute for the law of excluded middle in implicational propositional calculus.
- Consider Peirce's law, . If Q is true, then is also true so the law reads "If truth implies P then deduce P" which certainly makes sense. If Q is false, then so the law reads , which is intuitionistically false but equivalent to the classical axiom .