|Rules of inference|
|Rules of replacement|
In predicate logic, existential instantiation (also called existential elimination) is a valid rule of inference which says that, given a formula of the form , one may infer for a new constant or variable symbol c. The rule has the restriction that the constant or variable c introduced by the rule must be a new term that has not occurred earlier in the proof.
In one formal notation, the rule may be denoted
where a is an arbitrary term that has not been a part of our proof thus far.
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