Idempotency of entailment
2002370
190776564
2008-02-12T02:02:11Z
Gregbard
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{{Confusing|date=December 2006}}
'''Idempotency of entailment''' is a property of [[logical system]]s that states that one may derive the same consequences from many instances of a hypothesis as from just one. In sequent calculi this property can be captured by a [[structural rule]] called '''contraction''' and in such systems one may say that entailment is idempotent just in case contraction is an [[admissible rule]].
Rule of Contraction: from
A,C,C -> B
is derived
A,C -> B.
Or in [[sequent calculus]] notation,
:<math>\frac{\Gamma,C,C\vdash B}{\Gamma,C\vdash B}</math>
[[Category:Logic]]
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