\begin{definition}[Definition:Language of Predicate Logic/Alphabet]
The alphabet $\AA$ of the language of predicate logic $\LL_1$ is defined as follows:
<section notitle="true" name="tc">
=== Letters ===
The letters of $\LL_1$ are separated in three classes:
* variables;
* predicate or relation symbols;
* function symbols.
Each of these three classes is handled differently by the formal grammar of predicate logic.
\end{definition}