LPL 6.4-6.6 lecture

LPL 6.4-6.6 lecture - Sub-proofs, strategy, logical truth...

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Sub-proofs, strategy, logical truth Subproofs : Many of the proofs we will consider will require the use of sub-proofs. The reason that subproofs are helpful, and sometimes necessary, is that the consideration of hypothetical cases can lead you to steps in the proof that would be difficult to get otherwise. When should sub-proofs be used? At this point in the course, with only formal rules for the Boolean connectives and the identity symbol, there are only a few specific cases in which sub-proofs will be needed. Elim (proof by cases) Applying the Elim rule will always require the use of sub-proofs. If you see that one of your premises is a disjunction, it is likely that you will need to build sub-proofs so that you can eventually apply Elim to the disjunction. ¬ Intro (indirect proof) Like Elim , applying the ¬ Intro rule will always require the use of subproofs. If you see that your desired conclusion is a negated statement, or it contains material not found in your premises, then it is likely that sub-proofs
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LPL 6.4-6.6 lecture - Sub-proofs, strategy, logical truth...

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