Law of Identity/Formulation 2/Proof by Truth Table

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Theorem

Every proposition entails itself:

$\vdash p \implies p$


Proof

We apply the Method of Truth Tables to the proposition.

As can be seen by inspection, the truth value under the main connective is $\T$ throughout.

$\begin{array}{|ccc|} \hline p & \implies & p \\ \hline \F & \T & \F \\ \T & \T & \T \\ \hline \end{array}$

$\blacksquare$


Sources