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Elementary Logic

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Relating the <strong>Logic</strong>al Connectives<br />

Lemma<br />

|= (A ↔ B) ↔ ((A → B) ∧ (B → A))<br />

|= (A → B) ↔ (¬A ∨ B)<br />

|= (A ∨ B) ↔ ¬(¬A ∧ ¬B)<br />

|= ⊥ ↔ (A ∧ ¬A)<br />

Note: these equivalences imply that some connectives could be<br />

dispensed with. We normally want a smaller set of connectives when<br />

analyzing properties of the logic and a larger set when actually using<br />

the logic.<br />

Yih-Kuen Tsay (SVVRL @ IM.NTU) <strong>Elementary</strong> <strong>Logic</strong> FLOLAC 2011 19 / 64

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