Propositional logic/De Morgan's laws/Proof/Exercise

Prove, with help of truth tables, the De Morgan's laws, namely that the statements

$\neg {\left(\beta \vee \gamma \right)}\leftrightarrow {\left(\neg \beta \wedge \neg \gamma \right)}$

and

$\neg {\left(\beta \wedge \gamma \right)}\leftrightarrow {\left(\neg \beta \vee \neg \gamma \right)}$

are tautologies.

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