Rule of Association/Conjunction/Formulation 1/Proof 2

Theorem

$p \land \left({q \land r}\right) \dashv \vdash \left({p \land q}\right) \land r$

Proof

We apply the Method of Truth Tables.

As can be seen by inspection, the truth values under the main connectives match for all boolean interpretations.

$\begin{array}{|ccccc||ccccc|} \hline p & \land & (q & \land & r) & (p & \land & q) & \land & r \\ \hline F & F & F & F & F & F & F & F & F & F \\ F & F & F & F & T & F & F & F & F & T \\ F & F & T & F & F & F & F & T & F & F \\ F & F & T & T & T & F & F & T & F & T \\ T & F & F & F & F & T & F & F & F & F \\ T & F & F & F & T & T & F & F & F & T \\ T & F & T & F & F & T & T & T & F & F \\ T & T & T & T & T & T & T & T & T & T \\ \hline \end{array}$

$\blacksquare$