How many of the following statements is/are correct?

P. $A \subseteq B$ if $a \in A \Rightarrow a \in B$.

Q. $A$ is a subset of $B$ if $a$ is an element of $A$ implies that $a$ is also an element of $B$.

R. $\emptyset$ is a subset of every set.

S. Every set $A$ is a subset of itself.