3 Matching Annotations
 Jul 2020

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In logic, functions or relations A and B are considered dual if A(¬x) = ¬B(x), where ¬ is logical negation. The basic duality of this type is the duality of the ∃ and ∀ quantifiers in classical logic. These are dual because ∃x.¬P(x) and ¬∀x.P(x) are equivalent for all predicates P in classical logic


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Willard Van Orman Quine insisted on classical, firstorder logic as the true logic, saying higherorder logic was "set theory in disguise".

 May 2020

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