nLab exchange rule

Idea

In logic, the exchange rule or permutation rule states that the order of the premises is irrelevant to the validity of a deduction. Along with the weakening rule and the contraction rule, it is one of the most commonly adopted structural rules.

This rule is commonly discarded in natural language parsers, such as those built on categorial grammars or similar, such as link-grammar. This is because in most natural languages, word-order matters; the proper “deduction” or parse of a sentence depends on the order of of “premises”/words.

Statements

Exactly how this looks depends on the logic used.

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