Definition:Universal Closure of Well-Formed Formula

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

Let $\mathbf A$ be a well-formed formula of $\mathcal L_1$.

A universal closure of $\mathbf A$ is a sentence $\mathbf B$ of $\mathcal L_1$ of the form:


 * $\forall x_1: \cdots \forall x_n: \mathbf A$

By definition of sentence, this means that at least the variables occurring freely in $\mathbf A$ should be quantified over.