Definition:Free Occurrence

Definition
Let $\mathcal L_1$ be the formal language of predicate calculus.

Let $\mathbf A$ be a WFF of $\mathcal L_1$.

An occurrence of a variable $x$ in $\mathbf A$ is said to be a free occurrence iff it is not bound.

Also see

 * Occurrence
 * Bound Occurrence, the complementary notion
 * Alphabetic Substitution