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Existential Quantifier ∃

A formula that uses a existential quantifier expresses there exists a value with a particular property.
For example, (E. x (= (* (2) x) (6))) means that there exists some number x for which (= (* (2) x) (6)). Existential quantifiers are part
of predicate calculus.

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Definition

The existential quantifier is defined using the universal quantifier as
(<-> (E. x ph) (-. (A. x (-. ph)))) /edit/peano_new/predicate/predicate.gh/df-ex.

Predicate calculus