First-order logic

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First-order logic (FOL) (also called first-order predicate calculus (FOPC)) is a formal language incorporating predicate symbols, function symbols, constant symbols, variables, logical connectives and quantifiers, which can be used to express facts about a world. Unlike propositional logic (also known as “sentential logic”), FOL can express general statements or statements about existence, by using quantified variables. “First-order” means that statements which quantify over predicate and function symbols are not allowed.

CycL is not FOL because it does allow quantification over predicates and functions.

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