Here we introduce two more formal symbols. Consider the following propositions:

$ $

The last two propositions are combinations of the two first. $R$ is true if and only if both $P$ and $Q$ are true. We call this a conjunction, and represent it by the following:

$R \equiv P \land Q$

Similarly, $S$ is true if $P$ is true, or if $Q$ is true, or if both are true. $S$ will be false only if both $P$ and $Q$ are false. We call this a disjunction, and represent it by the following:

$S \equiv P \lor Q$