Logic / Unit 5 Logic 211 short lesson, about 20 seconds
Material Equivalence
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The idea
p ≡ q :: (p ⊃ q) · (q ⊃ p), and p ≡ q :: (p · q) ∨ (~p · ~q).
In practice
A biconditional unpacks as two conditionals, or as both-true-or-both-false.
Where people slip
Choose the unpacking the proof needs: conditionals for MP work, disjunction for DS work.
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