Existential instantiation
In predicate logic, existential instantiation (also called existential elimination)[1][2][3] is a valid rule of inference which says that, given a formula of the form , one may infer for a new constant symbol c. The rule has the restrictions that the constant c introduced by the rule must be a new term that has not occurred earlier in the proof, and it also must not occur in the conclusion of the proof.
Transformation rules |
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Propositional calculus |
Rules of inference |
Rules of replacement |
Predicate logic |
In one formal notation, the rule may be denoted by
where a is a new constant symbol that has not appeared in the proof.
References
- Hurley, Patrick. A Concise Introduction to Logic. Wadsworth Pub Co, 2008.
- Copi and Cohen
- Moore and Parker
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