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Destructive dilemma〔Hurley, Patrick. A Concise Introduction to Logic With Ilrn Printed Access Card. Wadsworth Pub Co, 2008. Page 361〕〔Moore and Parker〕 is the name of a valid rule of inference of propositional logic. It is the inference that, if ''P'' implies ''Q'' and ''R'' implies ''S'' and either ''Q'' is false or ''S'' is false, then either ''P'' or ''R'' must be false. In sum, if two conditionals are true, but one of their consequents is false, then one of their antecedents has to be false. ''Destructive dilemma'' is the disjunctive version of ''modus tollens''. The disjunctive version of ''modus ponens'' is the constructive dilemma. The rule can be stated: : where the rule is that wherever instances of "", "", and "" appear on lines of a proof, "" can be placed on a subsequent line. ==Formal notation== The ''destructive dilemma'' rule may be written in sequent notation: : where is a metalogical symbol meaning that is a syntactic consequence of , , and in some logical system; and expressed as a truth-functional tautology or theorem of propositional logic: : where , , and are propositions expressed in some formal system. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Destructive dilemma」の詳細全文を読む スポンサード リンク
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