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This chapter delves into advanced strategies and derived rules for logical reasoning and proofs. It introduces techniques such as the Hammer strategy, the Or-Out strategy, and several other strategic approaches (e.g., Backwards Strategy, Reductio) that facilitate logical deductions. The section on derived rules includes discussions on one-way and two-way rules such as Distribution, Disjunctive Syllogism, Modus Tollens, and DeMorgan’s Laws. The chapter concludes with practice problems designed to strengthen your command of these derived rules and logical strategies, enabling deeper understanding and application in proofs.
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Chapter 6: Strategies and Derived Rules 80-210: Logic & Proofs July 14, 2009 Karin Howe
Using Strategies Strategically • HAMMER!! first (&ER, &EL, E) • Is your goal the consequent of a conditional, but you don't have the antecedent available on other line? Apply E forwards to get the antecedent as a goal line. • Or-Out Strategy • Poof Variant on Or-Out Strategy • Backwards Strategy • Arrow-In Strategy • Reductio Strategy • Reductio Variant on Arrow-In Strategy
A Smaller Bag of Tricks • Distribution: (Distr&, Distr&C, Distr, DistrC) • Disjunctive Syllogism: (DSR, DSL) • Modus Tollens: (MT) • Hypothetical Syllogism [Chain Argument]: (HS) • Exportation [Ham & Eggs]: (Exp&, Exp) • Definition of the Conditional and Negated Conditional [Arrow Rules]: (DefE, DefI, E, I) • DeMorgan's Laws: (DeM) • Transitivity [Contraposition]: (Trans) • Double Negation: (DNE, DNI)
Let's Practice! • Deriving the Derived Rules • Practice Problems • Lab